All attempts to install new templates/main page fail (sorry, can't edit the title!)

Firstly, I love this software and only see it getting better and better.

I hope this is a simple problem because the behaviour is so global.  I tried to install 3 new templates and also a vazco_mainpage plugin and all resulted in a mis-configured plug-in error.  I am pretty sure it is on my end somewhere if all these are failing.

I am running: Release - 1.5, Version - 2009031301

Many thanks for any help!