Generating Huge String?

I have tried using chunks technique when creating huge string for a stored 
procedure (C code). I work like charm for small string, but when i create 
large strings i get a "server closed the connection unexpectedly" :-( I use 
palloc and repalloc for memory handling. Note! I made a standard C program 
that just keept on making the chunk larger (read string), i never did crash 
any. So what is postgres doing? (ps. the same happens if I use standard malloc 
an realloc)

Any ideas why? (No continues block of memory is large enough or?)
And how does one normally handle Large strings in postgres?

\Steffen Nielsen