Server Errors

Code	Most likely cause
400	Controller failed to return valid set of sources to serve
500	Minifier threw exception (e.g. JSMin choked on syntax)

You can find details by enabling FirePHP logging:

Install/enable FirePHP.
Open Firebug's console
Set $min_errorLogger = true; in min/config.php
Reload the Minify URL

Hopefully you'll see the error appear:

Minify: Something bad happened!

Javascript/CSS Problems

When Javascript errors occur, or URIs in CSS files are incorrectly rewritten, enable "debug mode" to ease debugging combined files:

Set $min_allowDebugFlag = 'true' in min/config.php
Append &debug to the Minify URI. E.g. /min/?f=script1.js,script2.js&debug (or use the bookmarklet provided by /min/builder/)

In "debug mode":

comments are inserted into the output showing you line numbers in the original file(s)
no minification is performed
In CSS, URI rewriting is performed
In CSS, a leading comment shows how URIs were rewritten.

Example: a combination of two Javascript files in debug mode

/* firstFile.js */

/* 1  */ (function () {
/* 2  */ 	if (window.foo) {
...
/* 11 */ })();

;
/* secondFile.js */

/* 1   */ var Foo = window.Foo || {};
/* 2   */
...

Example: Top of CSS output in debug mode

docRoot    : M:\home\foo\www
currentDir : M:\home\foo\www\css

file-relative URI  : typography.css
path prepended     : M:\home\foo\www\css\typography.css
docroot stripped   : \css\typography.css
traversals removed : /css/typography.css

file-relative URI  : ../images/bg.jpg
path prepended     : M:\home\foo\www\css\..\images\bg.jpg
docroot stripped   : \css\..\images\bg.jpg
traversals removed : /images/bg.jpg

Tips for handling Javascript errors

Use the latest version (2.1.4 beta as of Dec 2010)
Try debug mode to make the combined file more readable (and error locations findable)
Find out if other browsers have the same error
For pre-minified files, make the filenames end in .min.js or -min.js, which will prevent Minify from altering them
Test your scripts in JSLint.

Server Errors

Javascript/CSS Problems

Tips for handling Javascript errors

See Also