.NET Parser Error: Cannot Load Type ''...Global_asax"

Question

I am encountering an error described by the event viewer as a parser error.

Exception information: 
Exception type: HttpException 
Exception message: Could not load type 'MY_PROJECT_NAME.Global_asax'.
at System.Web.Compilation.BuildManager.ReportTopLevelCompilationException()

This happened seemingly with no changes to the system, as I was not working on this environment. I have gone and searched the Global Assembly Cache and found nothing in there, so it is not preferring the GAC name to my assembly as had been mentioned.

My research has suggested that this is some old assembly that has orphaned references, but I have found nothing of the like. How would one find these assemblies? I have tried restarting IIS and the entire machine as well. Not sure what else to try, any and all help would be greatly appreciated.

There is good logging in this project, but there is nothing in the logs at the warning or error level. So, it seems this occurs before any page is loaded by the system. IE, not in my VB backing scripts for the ASP pages, which would make sense if it's an assembly loading error.

For reference, this project is from the mid 2000s so there is quite a lot in here that predates my career as a developer.