Please help in running PPCHTeX

Hallo. 
 
I freshly installed in my Mandrake 10.1 Community system 
tetex-src-3.0.tar.gz in order to run PPCHTeX 
to type chemical structure formulas. 
Now, if I run TeX onto a file containing PPCHTeX pictures 
from within the directory /usr/local/teTeX/bin/i686-pc-linux-gnu, 
where the executable file `tex' is present, everything goes fine; 
instead, if I run TeX from my home directory, I get the message: 
 
! TeX capacity exceeded, sorry [text input levels=15]. 
 
Can anyone explain these two different behaviours  
and suggest how to work the problem out? 
 
Thanks in advance, 
Rodolfo Medina 
 



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