I'm going to bump this old topic, because I appear to be having the same problem and the suggestions here have not resolved the problem.
My spamcop.net account pops email from 8 different accounts. Two of them are yahoo.com accounts. Both are set up properly (as I read the FAQs). The server is popgate.cesmail.net. The username is my email address at yahoo (email[at]yahoo.com). The password is my yahoo password for that screenname.
The first account works perfectly. It always checks mail. Great!
The second account works only infrequently. For example, it has not been working for the past month. I have tried re-setting the password with Yahoo, and then changing the password saved in Spamcop, but that did not help. I tried deleting the account from my Spamcop options page, and then adding it again - no luck. The error it generates is "Invalid password", but I have just logged in and verified that the password is correct. It is a combination of numbers and letters, and is all lowercase... so it's not a caps lock problem, either.
The strange part is that occasionally (in the past) when I reset the password, it will work. However, it would only pop mail once or twice before generating Invalid password errors again. I've changed passwords on this account numerous times over the past few months, and I've been met with occasional, temporary success. However, I now can't get it to pop... no matter what I try.
I am almost certain I never signed up for any beta test with yahoo on this account. I've trolled my yahoo preferences for it, and I can't find anything to turn off to go to "classic" mode... If this is the problem, can someone give me guidance where to look for this in the yahoo prefs?
I'd appreciate some guidance on this bizarre situation.