UWL Error occurs repeatedly

Hi Friends,

While approving the requests in UWL(universal worklist) under Tasks tab frequently ( every 5 or 10 minutes),uwl throughs

bellow errors

1)Unable to perform the request.Try again and problem persists,inform your system administrator.

2)The item is no longer valid.Select another item or refresh the item list view.

Version:

NW-04s,EP 7.0 with SP15

Thanks

Srikanth