Debug: w3w.exe can't attach to the process. Access denied

Trying to debug the sharepoint but got error to attach to the process w3w.exe.

Take a look if the process is used by (TYPE) workflow. If that is the case, restart iis and make sure that worflow is not using w3w anymore.

Can't tell why it works such way. From my perspective, definitely bug but you have to get use it.