error 20700 while translating tracks

[StiffMittens]

I've seen several threads (on this site and others) relating to this issue, but so far none of the advice I've tried from those threads helps.

A session file which had previously behaved normally, I am suddenly getting this error when saving:

"Could not save as [session name] because (20700) while translating Tracks."

There is also a similar error when auto-backup tries to save a copy.

I have tried: trashing preferences, disabling plugins, going back to an earlier version, checking disk permissions and file system integrity.

Does anybody actually know what the error number 20700 refers to? Maybe if I knew what specifically the error is, I could figure out a solution.