If indeed the only change is the OS, then I see a couple of places to go look:
- You no longer have the proper permissions to write the new log file (which, in fact is what your error messages says!)
- Some Process has the log open and has not been properly fitted out with 'close and re-open on my signal' logic.
- This being Windows, trying to read a file that someone else has open for writing can be problematic (see the previous bullets)
- Your old system was taking advantage of a 'Windows Quirk' (I have been told to stop calling them (adjective) Windows Bugs). That 'quirk' has been patched in the new OS.
- And, the ever popular solution -- "Murphy hates you"
If it was me, I'd start with the Permissions issue first.
Good luck, this is likely not to be the first 'OS quirk' issue you are going to run into. (Ask me sometime why I hate upgrading Operating Systems. Preferably sometime when we both have a stein of beer at hand and the night is young....)
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I Go Back to Sleep, Now.
OGB