I came across this issue the other day while preparing for a Lunch & Learn for our support guys on Smart Access with Access Gateway. While I was clearing out some configurations in the AMC, this error popped up while trying to delete a web resourse. Not very informative.

The web resource was of type Citrix Web Interface 4.2 or later.

Running AAC 4.5 AAC450W004 (latest verion/patch), so thought I'd be ok.
After looking at my policies, filters to see if there was any references I found that the resource was still tied to the
XenApp farm at the AAC farm level.

AAC Farm -> Presentation Server Farms -> Web Interface

Once I unassociated the web resource from the XenApp farm I was able to delete it.
Knowledge Center article on the way...

David
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