Hi Chalapathi,
I've had exactly the same issue, this happens due to the new design in 10.1 where schedule lines (go through the legal control check). Your SA must be huge (including schedule lines).
While you try to create the import declaration, data is still being transferred in the background, basically this is a performance issue because transferring so much data takes a while. SAP released lots of notes to fix, please see this blog.
Latest notes/KBAs released in the Compliance area
Thanks,
Satish