Many thanks, Ron!!! I was able to open my file in the 602Tab application from Software 602 PC Suite,
http://www.software602.com. The charts still caused problems, but I was able to retrieve all data sheets in my workbook. I did have to use Task Manager to end the graphing task MGRAF.EXE several times before I could gain control of the program and save the file as an XLS.
I feel that one of two things happened that corrupted this file. 1. I had screwed up a reference on one of my controls or had too many controls on a chart. 2. I had deleted about 1000 rows of data from one sheet prior to my problems. When I saved the changes, I used Save rather than Save As. I thought perhaps there were some issues with writing the same file name with substantially less data. My charts had a number of controls from the Forms toolbar. Perhaps they were too complex to open in 602Tab.
In my case, using 602 retrieved substantially more data than the recovery utilities sold for this purpose. My recovered copies had many formulas converted to values.
All in all, this error cost me about 15 hours of development time, but my regenerated spreadsheet is better written and more cohesive. And the experience brought my attention back to my backup plan.
Save every 15 minutes.
Save As with revision number every hour.
Exit program and reopen file after every Save As. In my situation Excel continued to function normally even though the file it had written to disk would not open.
Replicate files to second computer every 8 hours
With this method I should never lose more than 1 hours work unless I suffer a catastrophic equipment failure in which case I could lose up to 8 hours.
I highly recommend that others keep 602Suite in mind if they ever encounter problems opening a file.