Question: I removed an extension from RefineryCMS but the tab for that extension is still in RefineryCMS admin area.

Answer: 
You are having trouble running "convert" because the PHP function exec() has been disabled in your php.ini file. 

When a exec() command is failing there are multiple steps that can be taken to troubleshoot the problem:

1. Verify if safe mode is on. Specifically the docs say:

> 
> Note: When safe mode is enabled, you can only execute files within the
>  safe\_mode\_exec\_dir. For practical reasons, it is currently not allowed
>  to have .. components in the path to the executable.
> 
> 
>
2. Turn on Error Reporting too see if that gives any more information. This can be accomplished by adding code like the following to the top of your script:

```
ini_set('display_errors', 1);
ini_set('error_reporting', E_ALL);

```
3. Simplify the exec() command to something that should always work:

```
exec('/bin/echo helloWorld',$output);
var_dump($output);

```

In your specific case when you tried step #3 above, it returned null. Null is what PHP returns when the exec() function is disabled. Also, if you were able to turn on error reporting (step #2) the output would have looked something like the following:

```
PHP Warning:  exec() has been disabled for security reasons in /home/path/to/file.php on line 2
NULL

```

The solution to this problem is to enable the exec function in php.ini or go to a host/server that allows the function to be used.
Try explicit error reporting: `error_reporting(E_ALL)`, maybe it gives warnings about exec permissions.

Also: With "Permissions for root catalog" you mean the folder from where you are executing and saving the files?