This error does not occur in all situations. It only occurs with certain files and with certain keywords. I have produced a test case that might help you, and can send anyone who wants it the resulting indexes.

Starting with the source code of swish-e, swish-e-2.4.2/prog-bin Created two subdirs that contain a subset of the files. 

I have narrowed it down to one set of files that works, and another that does not work, 

ls3122:~/swish-e-2.4.2/prog-bin # ls test12
	Makefile  spider.pl

ls3122:~/swish-e-2.4.2/prog-bin # ls test13
	Makefile  spider.pl  spider.pl.in

Indexing of those directories :

ls3122:~/swish-e-2.4.2/prog-bin # swish-e -i test12 -f test12.index
	Indexing Data Source: "File-System"
	Indexing "test12"
	Removing very common words...
	no words removed.
	Writing main index...
	Sorting words ...
	Sorting 1,303 words alphabetically
	Writing header ...
	Writing index entries ...
	  Writing word text: Complete
	  Writing word hash: Complete
	  Writing word data: Complete
	1,303 unique words indexed.
	4 properties sorted.                                              
	2 files indexed.  76,979 total bytes.  10,594 total words.
	Elapsed time: 00:00:00 CPU time: 00:00:00
	Indexing done!

ls3122:~/swish-e-2.4.2/prog-bin # swish-e -i test13 -f test13.index
	Indexing Data Source: "File-System"
	Indexing "test13"
	Removing very common words...
	no words removed.
	Writing main index...
	Sorting words ...
	Sorting 1,303 words alphabetically
	Writing header ...
	Writing index entries ...
	  Writing word text: Complete
	  Writing word hash: Complete
	  Writing word data: Complete
	1,303 unique words indexed.
	4 properties sorted.                                              
	3 files indexed.  142,443 total bytes.  19,606 total words.
	Elapsed time: 00:00:00 CPU time: 00:00:00
	Indexing done!


ls3122:~/swish-e-2.4.2/prog-bin # swish-e -w test -f test13.index

	Warning: Failed to uncompress Property. zlib uncompress returned: -5.  	uncompressed size: 105 buf_len: -19960

	# SWISH format: 2.4.2
	# Search words: test
	# Removed stopwords: 
	err: no results
	.

ls3122:~/swish-e-2.4.2/prog-bin # swish-e -w test -f test12.index
	# SWISH format: 2.4.2
	# Search words: test
	# Removed stopwords: 
	# Number of hits: 2
	# Search time: 0.000 seconds
	# Run time: 0.020 seconds
	1000 test12/spider.pl "spider.pl" 65479
	852 test12/Makefile "Makefile" 11500
	.


if I run hexdump on the index.property file, and the diff the two, it gives me this result :
ls3122:~/swish-e-2.4.2/prog-bin # diff -u test13.index.prop.txt 	test12.index.prop.txt 
	--- test13.index.prop.txt       2004-07-05 17:24:19.000000000 +0200
	+++ test12.index.prop.txt       2004-07-05 17:23:36.000000000 +0200
	@@ -1,9 +1,7 @@
	-0000000 0000 0000 e940 d771 000f 6574 7473 3331
	+0000000 0000 0000 e940 dd71 000f 6574 7473 3231
	 0000010 4d2f 6b61 6665 6c69 0865 0000 0000 0000
	-0000020 2c00 08ec 0000 0000 4000 71e9 13ad 7400
	-0000030 7365 3174 2f33 7073 6469 7265 702e 2e6c
	-0000040 6e69 0008 0000 0000 0000 b8ff 0008 0000
	-0000050 0000 e940 c071 0010 6574 7473 3331 732f
	-0000060 6970 6564 2e72 6c70 0008 0000 0000 0000
	-0000070 c7ff 0008 0000 0000 e940 ad71          
	-000007c
	+0000020 2c00 08ec 0000 0000 4000 61e9 10ee 7400
	+0000030 7365 3174 2f32 7073 6469 7265 702e 086c
	+0000040 0000 0000 0000 ff00 08c7 0000 0000 4000
	+0000050 61e9 00ee                              
	+0000053

It also does not occur on all the words.
But all the words are the same in both indexes : 
	swish-e -k* -f test13.index > test13.words
	swish-e -k* -f test12.index > test12.words
	diff test12.words test13.words
Produces no difference.


If it look for the work, make, I get no errors.
ls3122:~/swish-e-2.4.2/prog-bin # swish-e -w make -f test13.index 
	1000 test13/spider.pl "spider.pl" 65479
	1000 test13/spider.pl.in "spider.pl.in" 65464
	645 test13/Makefile "Makefile" 11500
.
ls3122:~/swish-e-2.4.2/prog-bin # swish-e -w make -f test12.index 
	1000 test12/spider.pl "spider.pl" 65479
	645 test12/Makefile "Makefile" 11500


So I also tried the test 14 with just spider.pl and spider.pl.in
swish-e -w test -f test14.index 
	1000 test14/spider.pl "spider.pl" 65479
	1000 test14/spider.pl.in "spider.pl.in" 65464

and test15 with spider.pl.in and Makefile
swish-e -w test -f test15.index
	1000 test15/spider.pl.in "spider.pl.in" 65464
	852 test15/Makefile "Makefile" 11500

please tell me if you have any ideas how to approach this problem, and if you want me to send you a tarball.

Mike