fatal error when installing theme

I am currently working with joomla and finding it very anoying
I had a problem with the back end so had to reinstall it
I backed up my theme but when I went to put it back in and use it I got this error
Fatal error: Call to undefined method stdClass::replaceMootools() in /mounted-storage/……/mysite/joomla/templates/my_template/config.php on line 54
I have been asked to move the theme from version 1.5 to 2.5 and its causing me nothing but difficulty
line 54 is this…
fatal error when installing theme

See original post by saturn100