I get the same fault with Win 7 x64. I carefully select one only of the files in the Blink list, click on the Blink File Move icon, select the existing destination folder and immediately get the error message. I've never used Blink File Move before so I don't know if it is a new 'problem'. I have the latest version of PI with all updates installed and I have a home-assembled PC, Intel i7 CPU and 32Gb RAM. The OP is using .fit files and mine was .xisf so no commonality there. We both live in Australia though! 8)
Charles