Office addins not being loaded

Office 2010

Spiratest V3.0

Latest versions of Spiratest addins and VSTO loaded.

The addins do not appear in Excel, Word or Project. I can see them in the addon management part of the office apps, but they are disabled. Enabling them and restarting the application just disables them again.

Th path to the addon looks like this:

C:\Program Files\Inflectra\Spira MS Office 2007 Add-Ins\SpiraExcelAddin.vsto|vstolocal

In the Com Add-Ins dialogue for Excel, it sometimes says it fails to load due to a runtime error. I don't see that in Word.

Enabling the addin, clicking OK, then going back to the add-in dialogue box shows the addin is again disabled. The checkbox setting doesn't seem to stick.

Any ideas?