sudden Acrobat failure – Save as .pdf hangs at generation of .tps

Yes, I know my set-up is obsolete to the point of dangerous … it has taken me months to get approval for new licences, and even now they've arrived I've been waiting since April for Central Support to install them. But, ancient software notwithstanding, everything has been working as expected until this afternoon. Starting from an FM 12 (non structured) file with one referenced graphic, I select File > Save as PDF … no "busy" cursor in FM, no Acrobat X Pro springing into life: just a 2,253K .tps file appearing in the file manager. I've got 5.48Gb spare on the networked drive, so I don't think that's the problem.

Update on "suddenly" – another .fm file distilled via Save as at 13:45 without any problems. After checking a few others, all of which failed after generating the .tps, I made a copy of this file and tried Save as again at 15:30. Failed.

Any hints/tips on solving this will be extremely welcome! Thanks in advance.