"The given assembly name or codebase was invalid." - Sitecron error in the log

[lreeder14]

Question: any ideas what could be causing this and any ideas for a solution?
We are on Sitecore 9.1.
From the Sitecron log file I believe it's telling me we're on version 3.1.0.0
7324 13:00:13 INFO Initialize SiteCron: 3.1.0.0

7324 13:00:39 ERROR SiteCron ERROR: The given assembly name or codebase was invalid. (Exception from HRESULT: 0x80131047)
Exception: System.IO.FileLoadException
Message: The given assembly name or codebase was invalid. (Exception from HRESULT: 0x80131047)
Source: mscorlib
at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMarkHandle stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName, ObjectHandleOnStack type)
at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName)
at System.RuntimeType.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark)
at System.Type.GetType(String typeName)
at Sitecron.Core.Jobs.SitecronJob.get_JobType()
at Sitecron.Core.Jobs.SitecronJobValidator.IsValid(SitecronJob job)
at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
at Sitecron.Core.DefaultScheduleManager.ScheduleAllJobs()