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As I'm updating my old scripts on rebol.org, I'm trying to understand 
the problems with compress/gzip & decompress/gzip , 
and found at least one issue in u-zlib.c . 

When compressing, as the checksum method is assumed to be adler32 
for most of the code, stream->adler (the current checksum) is wrongly 
initialized to 1 in two places, giving an off-by-one checksum in 
the output and making it unusable for decompress/gzip. 

Still no clue for what yields the 
     ** Script error: value out of range: none
error and why calling 
     compress "" 

seems to fix this problem sometimes.It seems that something isn't 
correctly resetted between calls.