I had the problem to, On the HTTP Filter, I deselected the following signatures. (I downloaded the scripts to create this from isaserver.org.)
Name: ScriptInject1
Description: Blocks 'StartOfTag left parentheses<right parentheses' in Request URLs
Search In: Request URL
Signature: <
Name: ScriptInject2
Description: Blocks 'EndOfTag left parentheses>rightparentheses' in Request URLs
Search In: Request URL
Signature: >
Note in the above script I used the word left parentheses for ( and right parentheses for ) as the combination is blocked on this site.