If we get the error while loading a vBulletin site,

"Content Encoding Error
The page you are trying to view cannot be shown because it uses an invalid or unsupported form of compression."

it is because we are GZIPPING the output twice. Probably on the webserver level and in vBulletin.

The solution is to turn off GZIP in vBulletin. For this follow:

1.
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Admin CP -> vBulletin Options -> Cookies and HTTP Header Options -> GZIP HTML Output -> No


Some times we won't be able to get into the admin page to do this. In that case, we would need to run a database query to alter the parameters.

For this, get into mysql prompt and switch to the database used by vBulletin. (Make sure to take a backup of the database before making the changes).

Then run the following query:

2.
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UPDATE setting SET value = '0' WHERE varname = 'gzipoutput';

UPDATE datastore SET data=REPLACE(data,'s:10:"gzipoutput";i:1;','s:10:" gzipoutput";i:0;') WHERE title='options';


If we are using a table prefix, those queries should be:


UPDATE bnvbsetting SET value = '0' WHERE varname = 'gzipoutput';

UPDATE bnvbdatastore SET data=REPLACE(data,'s:10:"gzipoutput";i:1;','s:10:" gzipoutput";i:0;') WHERE title='options';

We can also try the following instead of all the above mentioned fixes:

3. edit config.php and add

DEFINE('NOZIP', 1);
right under the <?php line to disable GZIP.