I haven't got an real answer to your problem, but what I think is hapening is that onmonitor is missing some libraries. Onmonitor itself is actually some kind of Informix 4GL program, and is now complaining about it's libraries.
However i don't know what you are planning to use onmonitor for. I wouldn't recommend using it on 9 engines. The reason is very simple: It isn't supporting all new features of 9, but is sometimes supporting 7 features which are already replaced or removed in 9. I also thought IBM was telling customers the same, as far as I'm concerned they may well remove it from their distribution.
All functionality you like about onmonitor is build in the 'new' ISA product. Which is web based an much more advanced. Of course also the old and low level command line utilities are still there.
I hope this is some kind of answer to your problem.