Thread:Project:Support desk/Upgrading error ERR CONTENT DECODING FAILED/reply (4)

Probably double gzipping, if you recently updated apache/php could be something with thier config (in particular, do you have stuff set in php's output buffering settings to gzip everything? zlib.output_compression etc. It could be misconfigured or something). Do you have $wgUseGzip enabled in LocalSettings.php (not that it should matter)? Do you have file cache enabled (although that shouldn't come into play during the upgrade script). What about $wgCompressRevisions (Also shouldn't matter, but just asking about the gzip related variables just in case)

Try setting $wgDisableOutputCompression = true; in LocalSettings.php and see if it affects anything (that disables MW's gzip support)

The weird part about this is you're saying this is happening run running the web updater, I would expect it to happen on all pages, or not at all.