Could not load all ISAPI filters for site ###. Therefore site startup aborted.

Whilst setting up a site on a 64bit server running IIS7.5, I was stumped with this error in the event log for a few hours “Could not load all ISAPI filters for site ###.  Therefore site startup aborted.” A quick search of Google resulted in a number of fixes, none of which helped.

My colleague and I eventually discovered that the error was caused by a setting the advanced settings section of the application pool. To fix this yourself complete the following steps:

  • Open IIS and navigate to the application pool in question.
  • Right click and select Advanced Settings…
  • In the (General) section locate “Enable 32-Bit Applications” and set this value to True
  • Click OK
  • Restart the web site