Hi,
1. Have to tried to switch the account to service user as suggested above? What were the findings?
2. I found these answers in other link for the same problem. Not sure if they are valid. Anyway I am copying them here.
a. Check dates in fields of table USR02. If someone played with these fields contents, it can cause issue.
b. If One user face the same, check USR02 --> TZONE & PWDDATE
Thanks.