When developling for SharePoint, I find myself always turning on the call stack and disabiling the custom errors in my development environment. It really does help when trying to debug run-time problems. I know there a few posts out there that describe how to do this, but I figured I would repost it as a reference for myself (which you are welcome to use).
Just remember that I do this in my development environment only. I don’t recommend changing the web.config files in any other environment.
Enabling the Call Stack
Set the value CallStack attribute in the SafeMode element in the web.config file to true.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<configuration>
...
<SharePoint>
<SafeMode MaxControls="200"
CallStack="true"
DirectFileDependencies="10"
TotalFileDependencies="50"
AllowPageLevelTrace="false">
...
</SafeMode>
...
</SharePoint>
...
</configuration>
Disabling Custom Errors
Set the value of the mode attribute in the customErrors element to Off.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <configuration> ... <system.web> ... <customErrors mode="Off" /> ... </system.web> ... </configuration>
Enabiling Compilation Debugging
Set the value of the debug attriute in the compilation element to true.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<configuration>
...
<system.web>
...
<compilation debug="true">
...
</compilation>
...
</system.web>
...
</configuration>
Putting it all together
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<configuration>
...
<SharePoint>
<SafeMode MaxControls="200"
CallStack="true"
DirectFileDependencies="10"
TotalFileDependencies="50"
AllowPageLevelTrace="false">
...
</SafeMode>
...
</SharePoint>
<system.web>
...
<customErrors mode="Off" />
...
<compilation debug="true">
...
</compilation>
...
</system.web>
...
</configuration>