This morning we went to post our GL Batches (GL-O) and everything appeared to work fine until it tried to finish printing to a text file.  We got an "Error opening file MKAHIST.BMM - 12" error message, and after selecting "OK" to continue we were back at the main Accounting menu.
 
This happens in both Classic with the 6/20 updates and in Evo

Yup!  It's there all right.  I went to check, then tried the report again.  Same results!
 
I even tried moving a copy of MKAHIST.BMM to the directory where I'm saving the report and freeing up substantial disk space on the drive, but still the same thing.

By printing to a text file, I mean we are attempting to print the report, but instead of a paper copy (which in our case would kill thousands of trees! Today's report was 211 pages and the one from the day we started having trouble was 69!)) we send it to a file for archiving. (options are to  List, Printer or File)
 
Yes, we can post them, and the text file I found is being created, but we never got the error message before!
 
As a side note, now that we've gone ahead and posted the offending transaction, I still get the same error message.