Office 2010 - SPO read only error / data loss
Doing an IE reset causes the office document cache handler add-on to be disabled. This add-on could also be disabled for many other reasons.
The office document cache handler add-on and the SharePoint OpenDocument Class add-on need to either be both disabled or both enabled. Otherwise we get the corrupt open and failed saves.
What I am calling a corrupt open is:
Doc looks to open fine, but when you save you get read-only error below, or if you close Excel (or other office app) via the X in upper right hand corner, Excel will ask if you want to save, you say yes, you get no error, but no save happens (data loss).
This behavior does not seem to impact SharePoint 2013 on premises servers. Enabling the office document cache handler add-on seems to make the issue go away.
"FullDocPath is read-only. To save a copy, click OK, then give the workbook a new name in the Save As dialog box."