What does tjis mean:
A level 0 archive of Root DBSpace will need to be done.

???

Just what is says. You have done something, like add or remove a dbspace, and Informix is telling you that in order to recover those changes it needs a new level 0 of root - where the sysmaster db is stored.

Happens (amongst other reasons) when you add/remove a chunk or create a dbspace. If you want to skip it, you can change your tape variable in onconfig to /dev/null on unix or NUL: in windows (yes with one L).