I assume you hit the MAX_PATH (260 characters) limit, which means
the amount of characters in the full path is not allowed to exceed 260 chars, might this be?
If so and because you are on windows 10 there MIGHT be a solution.
Stop npp and edit the registry
add a REG_DWORD variable called
LongPathsEnabledand give it a value of
1See here for the explanation of this.
Note, I don’t have any experience with this key but rumors on the web say
that 32bit applications might have issues when having set this key and using
api calls which do respect that key.
Cheers
Claudia