Hi fellow exceleites

I am writing a VBA moduel in excel 2003, which does certain calculations based on data in several sheets and displays a report in the last sheet(Tab).

I am getting this error :-

-2147417848
Automation error
The Object invoked has disconnected from its clients.

This error always occurs at the following line of code.

ThisWorkbook.Sheets("AE Pivot").Copy Before:=NewBook.Sheets(1)

After i click OK on error msg box, excel seems to get bugged up and shuts down itself and launches itself again with a new blank worksheet

And as if this wasnt enough this error doesnt occur evrytime, its quite moody,
occurs say once in 10-12 runs, but always on the same line of code.
Plzzzz help