Sania, I would suggest to not post the same question in different subspaces.
There's no special customizing on the WebUI for the copy control, so if works on SAP GUI and not in WebUI probably is due custom development. Can you try to disable the component enhacements and try again (I will find how to do it if you search)? I would also check if there's any BADI implementation which "messes up" the standard behaviour, as Rene already suggestes my first option would be any custom implementation of the CRM_COPY_BADI BADI.
Cheers!
Luis