Help on triggers

[singularity]

I need some input on this. I have an INSERT-trigger on an order table, but sometimes a record will be lost. I suspect that this is caused by the trigger causing an error, thereby rolling back the entire INSERT. But I can not find anything wrong with the SQL-code, and the values used in the INSERTs that fails are identical to the ones in those that go through.
The trigger is too long to paste in here, but can anyone give me any general tips on creating very large triggers, any pitfalls, etc.. Simply put, how can a trigger fail using the same parameters that work fine at other times.