I have an MS Sculpt Mobile Keyboard. It pairs fine and works, but after sleeping the computer for a long time and resuming, the keyboard loses connection. Disconnecting and reconnecting doesn't help. It needs to be re-paired.

I had wondered why my computer would not wake (via keyboard!) from sleep after a long time, though it would wake after a short period. This explains it. The keyboard loses connection and I have to resume my computer using the power button.

Any fix for this?

Does switching off (or removing the battery) otherwise clear the bad state which exists between the keyboard and computer?
It seems quite odd that a full-repairing would be required.

May the problem be with Bluetooth module either in the keyboard or in the pc?

If one wanted to diagnose that problem, it would be advisable to see if another bluetooth peripheral such as mouse experiences the same issue.