WebCore installation

I'm running into a
image
error, when trying to build or install FNC Core for WEB. This error is not specific enough, no idea which PATH exactly it refers to. I cannot see anything untoward in the Windows PATH, for instance.

Actual errors are:
Invalid characters in path
[
]
[Fatal Error] Invalid characters in path
[
]

Has anyone seen this before?

PS: Interestingly enough, I could install FNC UI Pack & Chart for WEB without any issues. I expected that Core was a pre-requisite. But apparently I may not even need it. Is this expected?