SSIS script task fails on server with error "Cannot load script for execution"

Microsoft made a breaking change to ScriptTasks between SSIS2008R2 and SSIS2012. Thankfully, the fix is very simple. Just replace this line:

? 1 [System.AddIn.AddIn("ScriptMain", Version = "1.0", Publisher = "", Description = "")] with this:

? 1 [Microsoft.SqlServer.Dts.Tasks.ScriptTask.SSISScriptTaskEntryPointAttribute] and everything should work for you as expect.

Can also be a version mismatch. If the SSIS project is set to target SQL Server 2012, but is deployed to a SQL 2016 instance then this error occurs. Change the target version in the project properties and redeploy.

So, the answer is unfortunately to rebuild the script task. It appears that these things can get corrupted. I literally did not change a single line of code, just recreated the task and copied the code from the broken version.