Hi !

Please DO NOT Edit the config.aspx file  (For v3.5 and v3.6)
You only need to edit the web.config file
All Installation instructions are located in the read me folder
In web.config file  you will find 
<!-- Enter customErrors mode="Off" to hide error from user -->
<!-- If a Error occur redirect user to a page -->
<customErrors mode="On" defaultRedirect="ErrDefault.htm"> 

Change it to  see the real error message this should only be used  during  debugging

<!-- Enter customErrors mode="Off" to hide error from user -->
<!-- If a Error occur redirect user to a page -->
<customErrors mode="Off" defaultRedirect="ErrDefault.htm"> 

Let us know if you have any further questions

Thanks
Kaleemsoft.com