How to enable debugging in WSS 3.0
Renaud Comte has a great tip on how to get the full ASP.NET errors appearing in WSS 3.0.
The detail is to add the following item to your Web.Config (C:\Inetpub\wwwroot\wss\VirtualDirectories\80):
<SafeMode MaxControls="200" CallStack="false" ...>
<!-- Becomes -->
<SafeMode MaxControls="200" CallStack="true" ...>
<customErrors mode="On" />
<!-- Becomes -->
<customErrors mode="Off" />
<compilation batch="false" debug="false">
<!-- Becomes -->
<compilation batch="true" debug="true">