proget Failed to process request. 'There was an error processing the request: Invalid API key.'

I recently setup Proget to try its nuget and chocolatey servers. Now when I try to publish packages to nuget feed through a teamcity build, I keep on getting error "proget Failed to process request. 'There was an error processing the request: Invalid API key.'.". I've made 100% sure that the name and password are working fine and specified API key as per Proget doco (i.e. username:password ) . THat feed already has one package which I published on the day I installed Proget for trying out. What could have gone wrong?

I found a work around.

• [1] I confirmed that my username:password combination is correct.
• [2] Then I renamed that original feed to feed_old (or whatever you want or even delete it if it doesn't have anything important in it) I had created for trying out and which wasn't allowing publishing through teamcity and giving the error message as per the question's message.
• [3] Created new feed with the name I wanted.
• [4] Confirmed that the username I was using in API key had necessary privileges to publish to this new feed I just created.
• [5] Then tested the publishing to this feed through teamcity and VOILA!! it worked.

I don't know why this happened in the first place though. It would be good to find out and be able to fix underlying reason rather than using the above mentioned workaround.