Bug Report: table not in XLS format error

I have been getting this error off and on all morning. I thought that it might be related to this thread but I am not so sure. It is intermittent, sometimes I regen one of the tables in the spreadsheet and it works but I get sevral VALUE# errors. Othertimes it makes no difference, I have a multiple tables in app but majority of the tables come from one spreadsheet in which the error is referencing. And it is definitely a xlxs