When I try to download LoTW QSLs from within CQRLog, I get the "...returned invalid adif file header. Your username/password could be wrong..." error, but I know that my username and password are correct.
 
If this is working for others, I wonder how many of those others have multiple call signs associated with their LoTW account?  I have 2 associated with mine, my original call sign and my current one, which I requested after upgrading my license.  If CQRLog isn't sending a call sign to download QSLs for, then that may be the cause of the error.  If it is the cause for the error, then at the very least the call sign set in the log configuration can be sent.
 
Let me know if you need any help from me in getting this working. In the meantime, at least manual download and import of the QSL info works.