I have been searching the web for an answer to my problem, but so far I have not been lucky.
I have create a custom workflow activity and I would like to debug it in visual studio 2010, but I don’t know how to do it.
Any help will be very much appreciated.
You have to attach visual studio to the process that is running on the server.
Here is the MSDN article on it
Some more resources regarding remote debugging:
Debugging with Visual Studio extensions for Windows SharePoint Services
Debug SharePoint Applications