Try unfreezing the panes (Window > UnFreeze Panes).
If that does not work please send me the file so I can see what the problem is
Shouldn't be a problem, just delete the sensitive info and send it out. I just want to see the structure of the sheet
Ok, go to www.wikisend.com and upload the file there (no need to sign up). You will then get a page that has the File ID and Download Link. Copy either the File ID or the Download Link and come back here and paste it in your reply.
hmm.. which sheet, which column, which cell?
I don't see any Dec 2010, and if type a value in any of the cells (say cell C41) nothing strange happens
Not doing that on this file. After typing in S57 and hitting Enter it goes to the next cell as it should