post upgrade cron run error

Yes, I have added a new table file_tmp to collect info about uploaded files which were viewed in the node preview but were never saved (user navigated away from that page) so that those files could be cleared later from the cron.

Since the module is still in active development and alpha stage, I didn't write a migration script at this stage. The new table should be created manually (or module uninstall and install back should do the trick, but the data will be lost).

okay, followed your instruction to create the table manually and it did work, no more erros.

I would write an update if I only knew how... or is there any reason not to write an update script?

Or in other words: deactivating module "file" and activating it again, does not create the tmp table in my case. (I switched to dev now.)

You should not just deactivate, but also uninstall the module and then install it back. Keep in mind that your existing files will get lost, so do it only on a test system.

Alternatively you can create a file_tmp table directly in the db. Table specifications are in the file.install file.