You need to set first debugging to ALL from Site administration > Development > Debugging
to get output for errors.
If your site does not have local distribution of latex and ImageMagick or Ghostscript installed tex filter is trying to use executable mimetex file (mimetex.xxx) from folder filter/tex that needs executable permission.
If it is not a permission issue there are still many reasons for this kind of issues, for example disabled functions of php or open_basedir restriction - but debugging should give more info...