you should not post problems with your custom code as mojoPortal bugs, this question should have been in the developer forum.
you need to understand how ASP.NET generates control ids, client ids must be unique for the entire page so asp.net makes them unique.
Especially in a grid control, the ids of controls in a row will be unique for each row, it cannot be otherwise.
so the server side id is not the same as the clientID of a control
in some cases you can use <%= JQGrid.ClientID %> but that only would select the table or the specific control it won't work as well for items in a grid.
probably you can solve it using class selectors instead of id selectors for jquery