Hello Guys , 
I'm encountring a very strange problem .

I created a user control and tested it as an ASP.NET control and worked well

thin I changed the parent control to [PortalModuleBase] to integrate it with DNN

then I add a new Module Definition and every things is nice untill now

I added this module to a page but I got an Exception : [Object Reference not set to an instance of an object ] without any details

I made debug but actually I didn't reach to my module control the exception raised before that and I couldn't know where

so how can I catch this error to know any details about it ???

Thank you so much MR.Wiliam
your answer helped me I checked event Viewer and I got it

I'm new to DNN that's why I forgot to use event viewer 

thanks a lot ;)