I was getting an error when downloading QSLs from eQSL, and followed advice given to someone else about running CQRLog from the console to see what the message was.  It appears that special characters in the parameters added to the URL being used to download the file aren't being properly escaped, and I was getting the error because my password contained some of them.  Changing my eQSL password to something that doesn't contain any URL special characters resolved the problem.