Error in execution of <bleachbit.Command.Function instance at 0x0409E170>

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Hi,

See the topic subject for error code.
I'm getting this warning when cleaning:
Windows 7 X64. This message shows in both 1.12 & 1.17 beta.
No such warning with Windows 10

Edit:

Seems to happen with the Firefox (Version 57.0) URL History box checked

Thanks,