SharePoint document library properties–The request was rejected by the HTTP filter

Weird error we have detected today. One of our platforms was published trough TMG, everything works fine when we tried to edit a column we got the following error:

“Error Code: 500 Internal Server Error. The request was rejected by the HTTP filter. Contact the server administrator.”

b1

Trying the same actions on any other list/library worked fine; just not for a document library.

The problem turned out to be related to HTTP filtering in TMG.

To fix the issue, Open the properties of the firewall policy.  Click Filtering > Configure HTTP under the Traffic tab.

b2

Uncheck Verify normalization.

b3

Save and apply changes and you should be all set.

Be aware that verify normalization will block URLs containing escaped characters after normalization.

Hope it helps!