Create table in functions

Hello,

I striped down my function up to a strange thing:

web=# create function pHelpTable( )
web-#   returns int
web-#   As '
web'#     Begin
web'#       Create Table Temp_NumTable  ( Num int ) ;
web'#   
web'#       return 17 ;
web'#     End; '
web-#   language 'plpgsql' ;
CREATE
web=# 
web=# select pHelpTable( );
ERROR:  copyObject: don't know how to copy 611
web=# 


What does this mean?  The ERROR is caused by the Create Table statement
(when I removed it from my complex function it worked well).
So why doesn't this work and what copy function fails here??

Kind regards
         Andreas.