[imp] MIMP only shows a blank page

[Yoseff Francus]

I seem to have MIMP configured, based on what horde tells me when I go to 
the Amdinistration - Configuration page. However, when I fo to

https://hostname/horde/mimp  all I get is a blank page. Similarly if I try 
to go to Mobile Mail from IMP I get a blank page.

Using Apache 2.2.4 and PHP 5.1.4

test pages all come up ok.