Call to undefined function phptemplate_get_ie_styles()

On a multi-site stack at a client, we were not able to run update.php anymore. The result was a WSOD (white screen of death). I tried to increase the php memory limit and disable my APC. But it didn't help.

When looking at the logs, the apache log didn't contain any error. But when looking at the php error log I found this error: 

Call to undefined function phptemplate_get_ie_styles() 
in /mystack/themes/garland/maintenance-page.tpl.php on line 23

I started my online investigation and found three possible causes:

• A lot of people had this error because they removed the Minelli theme from the core garland theme. Putting it back solved their error.
• Some others reported a problem because garland was in the core themes folder and also in the themes folder of a site in the multi-site stack.
• The last option was disabling modules until update.php works again.

In my case I found a copy of garland that was renamed and resided in a site of the multi-site stack. But trying to change code or remove the theme didn't really help.

In the end I started disabling modules and was lucky to immediately choose the right module: supercron. By disabling this module, update.php was working again. I'm posting this here to help people that may encounter the error in the future!

Edit: In the meantime this blog post has been picked up by Tim Millwood who saw this behavior on a site of a client. He logged an issue.