Inventor thumbnails missing in Windows Explorer: diagnosis and fix

You open a folder of Inventor parts and assemblies in Windows Explorer, in Large icons view: not a single thumbnail, only the generic Inventor icon.

The files involved are Inventor's: .ipt (parts), .iam (assemblies), .ipn (presentations), .idw and .dwg (drawings). Here are the possible causes, from the simplest to the most hidden, each with how to recognise it and how to fix it.

What you should see once the problem is solved:

How Explorer displays an Inventor thumbnail

Explorer cannot read an Inventor file. For each extension, it looks in the registry for a thumbnail handler: a DLL installed with Inventor that extracts the preview saved inside the file. It looks for it under the extension itself (.ipt), under the associated file type (Inventor.PartDocument, for example) and under SystemFileAssociations.

For a thumbnail to appear, thumbnails must therefore be enabled, the file must contain a preview, a handler must be declared, its DLL must exist and Windows must agree to load it. Every link in that chain can break.

1. Thumbnails are turned off in Explorer

Diagnosis: in Explorer, … menu → Options → View tab. If Always show icons, never thumbnails is ticked, no file has a thumbnail, not only Inventor files.

Fix: untick the option, then OK.

If the box is greyed out, or ticks itself again, a group policy enforces it: talk to your network administrator.

2. The thumbnail cache is stale

Windows keeps thumbnails in a cache. If it has recorded a file as "no preview", it does not ask again, even once the problem is solved.

Diagnosis: hard to establish on its own. That is why you clear the cache as a matter of course, and after each fix described below.

Fix: run Disk Cleanup (cleanmgr), tick Thumbnails, then OK. Then sign out of Windows and back in: Explorer does not always reload a handler while it is running.

3. The file contains no preview

The handler computes nothing: it displays the image Inventor saved inside the file. A file created by a batch process, for example, may not have one.

Diagnosis: open a part in Inventor, change it, save it. If that file shows its thumbnail and the others do not, it is the others that have no preview.

Fix: open and save those files again in Inventor.

4. The file is on a network drive or in OneDrive

A company policy can disable thumbnails on network folders, and a OneDrive or SharePoint file that is "available online only" shows none.

Diagnosis: copy a file to the desktop. If it shows its thumbnail there, the location is to blame.

Fix: for OneDrive, right-click the folder → Always keep on this device. For a network drive, talk to the administrator.

5. No handler is declared for the extension

Another application may have taken over the extension, or an old Inventor version left behind, when uninstalled, keys that lead nowhere. This is common for .dwg, which Inventor, AutoCAD and DWG TrueView all compete for.

Diagnosis: open the Registry Editor (regedit) and look for the following key, replacing .ipt with the extension at fault:

HKEY_CLASSES_ROOT\.ipt\ShellEx\{e357fccd-a995-4576-b01f-234630154e96}

That long identifier stands for thumbnail handlers. If the key does not exist, look at the (Default) value of HKEY_CLASSES_ROOT\.ipt: it gives the associated file type (for example Inventor.PartDocument). Then look for the same ShellEx\{e357fccd-a995-4576-b01f-234630154e96} subkey under that file type. If it exists in neither place, no handler is declared.

When it exists, write down its (Default) value: it is the handler's identifier (CLSID), a string of the form {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}. You will need it for the next two points.

Fix: right-click a file → Open with → Choose another app → your Inventor version → Always. If the key is still missing, run a repair of Inventor from Settings → Apps → Installed apps.

6. The handler's DLL no longer exists

Diagnosis: in the Registry Editor, open the following key, replacing {CLSID} with the identifier written down in point 5:

HKEY_CLASSES_ROOT\CLSID\{CLSID}\InprocServer32

Its (Default) value gives the path of the DLL. Check in Explorer that this file does exist. A path pointing to an uninstalled Inventor version, or to a drive that no longer exists, gives the problem away.

Fix: repair the installed Inventor version, as in point 5: it registers its handler again.

7. The handler is blocked by Windows

This is the sneakiest cause: everything is installed and declared correctly, but Windows has been told never to load this handler. No message says so. Such a block is often set to silence an extension that made Explorer crash or slow down, then forgotten; security software or a group policy may also have set it.

Diagnosis: Windows keeps this blacklist in two places, one for the whole machine, the other for the user:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions\Blocked
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions\Blocked

Open both keys in the Registry Editor. If either contains a value named after the CLSID written down in point 5, the handler is blocked.

Fix: remove that value from the list. Three ways to do it, your choice.

With ShellExView, without touching the registry. Windows offers no user interface to manage this list, but NirSoft's free ShellExView tool does: its Disable command adds an extension to the list, and Enable removes it.

1. Download the 64-bit version of ShellExView from the NirSoft website and run it as administrator.
2. Look for the lines whose Product Name column reads Autodesk Inventor and whose Type column reads Thumbnail: these are Inventor's thumbnail handlers. The Disabled column tells whether they are blocked (Yes) or not (No).
3. Select the blocked lines, right-click, then Enable Selected Items.

With the Registry Editor. In the relevant Blocked key, make a backup first (right-click the key → Export), then delete the value (right-click → Delete). Under HKEY_LOCAL_MACHINE, you need administrator rights.

From the command line, handy to fix several workstations. From a command prompt run as administrator, replacing {CLSID} with the identifier:

reg export "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions\Blocked" "%USERPROFILE%\Desktop\Blocked-backup.reg"
reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions\Blocked" /v {CLSID} /f

If the value is under HKEY_CURRENT_USER, replace HKLM with HKCU and run the command in the user's own session, without elevation: run by an administrator with their own account, it would change the administrator's registry.

If the value reappears after a restart or a gpupdate, a group policy or an antivirus enforces it: talk to the domain administrator. And if the block had been set on purpose, check afterwards that browsing your busiest Inventor folders stays smooth.

Summary

Cause	Diagnosis	Fix
Thumbnails turned off	No file has a thumbnail	Untick "Always show icons"
Stale cache	—	Disk Cleanup → Thumbnails
File without preview	A re-saved file has its thumbnail	Save again in Inventor
Network or OneDrive	A copy on the desktop has its thumbnail	Keep on device, or see the administrator
No handler	ShellEx\{e357fccd-…} key missing	Re-associate the extension, repair Inventor
DLL missing	InprocServer32 path not found	Repair Inventor
Handler blocked	CLSID in Shell Extensions\Blocked	ShellExView, regedit or reg delete

After each fix, clear the thumbnail cache and sign out and back in.