If you are using AMP prior to AMP 2.6 (yet to be released at time of writing) - you may get the following error when trying to install/update an application that uses SteamCMD:
Cached Credentials Not Found
This is caused by an update to SteamCMD whereby VALVe changed some of the messages used without warning. This message is actually a prompt to provide fresh login details, which AMP wasn’t aware of.
Solution
We’ve shipped an out-of-band update just to address this issue. Simply update AMP as normal. Quickest way is to simply run the following in a command prompt (Windows) or as a shell as the amp user (Linux)
ampinstmgr upgradeall