My old solution has been running in my intranet farm for a long time. The solution contains a feature which deploys a webpart. The webpart shows the users of a group, together with information from their user profiles.
I've done some pretty big changes to the solution, removing the old Visual WP and creating a new WP. I've removed the old WP from the feature, deleted it and added the new. The Feature has the same GUID.
I've tested the solution in a local, dev and QA env, all working out fine. When I tried to deploy to my prod. env., something went wrong. After deploying the solution, users are asked for credentials (but are not allowed to log in) in the whole web. app. I had to retract the solution again, and it seems like that fixed it.
I then tried to delete the WP on all pages where it was added. I deployed the solution, activated the feature without problems. When I added the WP to a page, the same thing happened again. Even farm accounts are not allowed to log in, so I don't think it's a permission issue either.
The way I'm redeploying is by retracting, installing the old solution, and then adding and installing the new solution. I'm not specifying any Upgrade actions - should I?