We are having problems running level 0 archives.
In the online.log file there were repeated "951" SQL error msgs.
The msg read: "User informix is not known on the database server".
I attempted to run a level 0 to /dev/null and received: "database is in an unstable state.", as an error msg.

Then we tried resetting the password for the user "informix" and this fixed the problem.

This will most likely be a problem at sites that implement password "aging".

finderr -951

-951 User username is not known on the database server. The database server that you tried to access does not accept either your user ID, the login name that is specified for the desired server host in your ~/.netrc file, or the user name that is specified in the USER clause of a CONNECT statement. If you are explicitly specifying your user name in the ~/.netrc file or in a CONNECT statement, check that the name is correct. If you do not have a valid user ID on the server computer, see your system administrator. This message appears with Version 6.0 and later.
-951 User is not known on remote host. This statement refers to a database on another computer system, but the other system does not accept your account name. You must have a valid login identity on any computer system you access. See your network administrator about getting a login ID. This message appears prior to Version 6.0.