Windows 7: Scanner vs W7x64

I don't know who's issue this is - so please point me.
Windows 7 - Canon - ME

Canon scanner with toolbox application.

Works fine mostly - periodically, it comes back with this error.

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CanoScan Toolbox
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Unable to scan. Make sure that there is enough space on the target disk.
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OK
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To clear it I must uninstall the qpp and reinstall it - good till the next time.
Sometimes I can clear it just by pointing to a different folder on the same or different drive. not this time.............

There is plenty of space on the HDD. like 426GB
Some suggested that going back to defaults on the app solved the issue - not for me.
Any Idea what is causing this.



BTW
thx