Sorry I have not had the time to test these workarounds yet... After spending half a day yesterday cutting out various combinations of usb sticks trying to narrow down the problem, which appears to be specific to Chromium out of all browser extensions in repository. At first the error message indicates write error and invalid media, so trying different sticks, etc...
However, since it appears this issue may surfice with some other extensions: Is there any across the board solution possible so TC base operation of backup function would not be affected by specifics of extension? In principle, this is a system/data backup function, therefore extensions should not be able to impact this operation? If some data or configuration file is or is not backed up to the extension's liking, then it is up to the extension to work or malfinction in consequence. The base system operation, such as backup, should not be prevented from working.
In a word, the user programs should not be able to prevent base system from correct operation... Is this correct thinking in modular architecture?