a trigger question

Hi,
i have a problem with "cache lookup failled" when an insert is made in a
table with a trigger.
Error message is : "ERROR : fmgr_info : function 16586 : cache lookup
failed"
Quest.: where this problem is ?
and where the documentation is on this subject ?.

I made :
GRANT ALL PRIVILEGES ON  all table and trigger,
trigger is a very simple program for cut string (OK when stand alone).

I am so sorry but beginers in english + beg. in trigger proc. + project'
stress = problem.
Thanks
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