Visual Studio 2012: Unable to attach the process. A debugger is already attached

Question

I built solution, created application in IIS and mapped it to the application folder. It works fine. Then I go to "Attach to Process", there are two w3wp.exe processes in list, but for one of them I get error "Unable to attach the process. A debugger is already attach." I've googled it but I can't find solution for my problem.

Answer 1

I have installed Debug Diagnostic Tool v2.0 and as a result I have Debug Diagnostic Service which is started automatically and attached to one of w3wp processes. After turning off and disabling this service all works fine. So the general rule: if you get such error check processes in task manager which can capture your w3wp process.

Answer 2

You have 2 instance of VS and two entries in IIS running on the same application pool, for instance Both Server and Intranet are running on the same application pool.

=> Solution open IIS :

° Select the site and click 'Basic Settings' : Here you can check/select the application pool used.

° Click on the "Application Pools" node (right under your computer name) => You get a list of defined application pools.

° Right click under the last one defined to open the context menu and select 'Add Application Pool...' Create a new name and give it the same parameters that the one that was used by your site.

° Select the 'Basic Settings' of one of your sites and change its application pool to the new one just created. => Now Server and intranet have different application pools and your can debug the both at the same time.

Hope this helps.

Answer 3

Debug Diagnostic Tool v2 Update 2

https://www.microsoft.com/en-us/download/details.aspx?id=49924

Can use this link if the link provided by @mtkachenko above doesn't work

Answer 4

Really odd - but this simple thing works for me:

1. Go to some file in your main project.

2. Go to Project menu and choose Set as start-up project.

This might seem redundant if you've already chosen that project as the start-up project before, but it seems to work.