I have had 3 unreadable content problems - 1 resulting in corruption , the other in repair , and the last in data save only .
1. Repaired without data loss = The xl/xalChain.xml problem was repaired by excel with the content was intact , with the loss of formatting only to the cells with the sumproduct formulas in them , even those this is a large extensive workbook with lots of macros. These were my only losses with this error that repaired itself.
Like you, this file was a template file. The calChain corruption, from what I can tell , occured during my beta testing of this file in which i imported data programically from a previous version of the template i was using.
To keep the file intact ( and it works now) , I cleared everything from the cells that had the sumproduct formulas ,and reentered them , and referenced them. ( they contained references to named ranges. ). So far so good.
2. Data loss resulted in complete corruption.
I received an unreadable content error, excel tried to repair it , etc. The repair failed and I lost everything. Luckily I had back up version and located the problem .
The problem was with a named range I was using within a table that over time was referenced to the wrong source. I deleted the named range , reentered it , now it works like a champ.
Named references can easily get screwed up if you import and export the information to and from other workbooks programically via copy/cut paste and do not clean ( ie apply and or reappy the reference to , and scope) the workbooks named range reference. OH I learned this the hard way.
3. The 3rd had to do with conditional formatting used within a table. The unreadable content was saved by giving me data only , loss of formats, data validations ,etc.
What I have found is if you move info around in a table via cut and paste with the table itself ,or from another source for reason i have yet to figure out the applied conditional formatting can get all screwy and refernce all kinds of cells and ofter re-references itself.
Once i cleaned this up by referencing the table itself instead of cells ( it will default back to a cell address but it does seem to remember the fact it should reference the table) . I did not have a problem again.
1. check named ranges
2. check formulas within a table , and the references
3. check table conditional formatting settings
Hope my trial and errors help you in someway.
take care,
Rachael