I wanted to tell you about two of my experiences with this error. It can be useful for some people.
Both times that gives me that error, I was trying to transfer the EAR from Quality environment to Production environment. Staring the deploy after the transport.
1. The first time the file system cache was full.
2. The second time, the error showed logon failure between the SDM and the File System, but the keys had not been modified. Only with restart the SDM It was enough.