Edited Issue: Categories creation error [201]

I'm having the following error when creating categories:

"Unhandled exception at line 422, column 25 in .../Administration/Projects/EditProject/1

0x800a138f - JavaScript runtime error: Unable to get property 'Webservices' of undefined or null reference"

the source of the error is the control "ProjectCategories.ascx"
and the instruction is:
window.BugNET.Webservices.BugNetServices.AddCategory(pid, name ,parentNodeId, function(result){
data.rslt.obj.attr("id", result); //set the new id to the new node
}, OnError);