Question : operation has been cancelled due to restrictions in effect

One of our clients has a SBS 2003 domain. All workstations are XP running IE 7. When they try to add goodsearch as search engine, they receive this message: "This operation has been cancelled due to restrictions in effect on this computer". What I did so far:
 
1. Try to disable anti virus software.
2. Logon administrator account.
3. Try different computers.
4. Try to reset IE.

Still receive this error. Could this be a group policy issue? If yes, where can I check or disable the policy? If not, what could be the problem?

Answer : operation has been cancelled due to restrictions in effect

blin2000--"where can I check or disable the policy"
If it is a group policy issue, You reach Group Policy (Editor) by Start|Run|type gpedit.msc |OK.  You will have to look around.