Debugging UDF’s is not quite as simple as debugging other SharePoint artefacts. The UDF is called by the Excel Services service application which runs as a separate process. Bearing this in mind we have two options, we can either attach our debugger to all instances of the w3wp.exe process, or we can find out which process is being used to run service applications on out server. Discovering the ProcessID used to run a User-Defined Function Even though I’m sure that everybody will take the lazy option of attaching to all worker processes, here’s how we can find out...