Shared Excel Workbook Jumbled

[tom1100]

We have been using a pair of shared Excel workbook to manage a production schedule for many years, and have had very few problems. Recently I noticed that we were running in compatibility format, and since everyone was using Excel 2007 I saved the workbooks in .xlsx format over the weekend when no one else had the workbooks open. I notified everyone of the change and updated the shortcuts they were using to open the files which are stored on our server. Things ran faster, but after a few days problems started to show up. Cells visible on one computer were not found on another computer even after reopening the file. Information entered in blank rows on one computer overwrites data when viewed on another computer. Reviewing the change history says the the old value was "blank" <BLANK>, but clearly some cells were overwritten. For example, today 9 rows of new data were added at the bottom on the worksheet by one user. When I open and view it only 3 rows of new data are at the bottom, and 6 rows have overwritten existing data several rows above. Those 6 rows are not all together. There are 3 rows in one spot, 1 row in another, and 2 rows further down. I am sure that data was overwritten because the other user enters data in columns B through G, and the existing data in column A is still there. Anyone have an idea what is going wrong? I would appreciate your help.