Excel - auto replication of data

Hi, I've been having a wierd problem on my Excel file (Excel 2003, SP3) that has worked fine until recently. When I input something into any cell in one worksheet, it gets replicated in the exact cell in all the other worksheets, and vice versa.

There is no noticeable linkages, circular loops, etc. Neither could I find any macro scripts in the background.

The above problem is not present in ealier backup copies of the same excel file. Any idea what is going on? Could the file be somehow corrupted?

Thanks DonkeyOte, you're a savior!!!!!