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Turn on your debugging system (something you should always do, preferably before posting)...
admin|system|preferences|General Settings
Do this for php debug and then try to do what you were indicating was causing a problem. Then do it for the MySQL debug (if you haven't figured it out yet). By running your procedure through each debug process, you should get a handle on what's going wrong (should...). The debug facilities in XOOPS are marvelous.
Then let us know what it says. But, by that time you will very likely have the knowledge you need to know what's wrong and possibly fix it.
Also, there are some bugs assoc with that module. Not sure what version you're using or if the bugs apply to you.
You could go
here and
here to make sure you have the latest and greatest versions.