Tried to enable wp-cache on word press tonight. Seems that the option to disable the gzip compression is missing from the settings/misc page. So to disable it (so you can enable wp-cache), I had to do the following:
1. Find the option number of the gzipcompression option in your wordpress table:
select * from wp_options where option_name='gzipcompression';
2. Update the option value to 0 (it is probably 1 now), use the option_id number you got from the first command:
update wp_options set optionvalue='0' where option_id='41';
Your gzipcompression should be disabled now and you should be able to enable wp-cache.