I installed Apache and found that it fixed the problem. I guess this means its something to do with IIS that's breaking things.

I get the same problem.

I'm running with the following setup, if its of any use to anyone.

Windows XP SP2
IIS 5.1
MySQL 4.0.22
PHP 4.3.9

Its a clean install from the xoops-2.0.7.3.tgz package. All I've done is run through the installation, and gone into the Admin section and tried to open one of the menu items.

I've tried to do this in both Internet Explorer 6 and Mozilla Firefox 1.0.

Also getting the following error:
Notice [PHP]: Undefined offset: 2 in file c:\inetpub\wwwroot\xoops\include\common.php line 267

Will report anything else I figure out to here.

Interestingly, the 2.0.9 beta reports 'Selected module does not exist!' instead of the error.

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Mat