I would recommend opening a support case to investigate further
We've seen some strange things with Orion asking for our username and pw over and over again. It comes and goes so I haven't investigated much yet.
Old post which has more than likely been resolved. Either way, this is my story!!!
So... Solarwinds support (FACE PALM) was no help. However, I had the same issue and my AD Admin account was locking out within seconds. I had to troubleshoot this with AD tools to first pinpoint the machine/server in questions. I then disabled all Solarwinds services and started them one by one trying a process of elimination. Finally, I created a service account to log in to the server and re-poll with instead of my AD Admin account.
If you've looked at all of the above you more than likely had nodes added that were being polled with your AD credentials. You can actually see how many nodes are assigned to specific credentials in the Orion GUI > Settings > Credentials > Manage Windows Credentials. Unfortunately it only gives you a count and not which devices as of version 2014.1.0 (Orion). I then went to my Windows nodes, Orion GUI > Settings > Node & Group Management > Manage Nodes > Windows, to mass updated the polling credentials. This resolved my issue that perplexed me for a few days...
Hope this helps someone else out there!!!