Script tasks are a great way to enrich your ETL, especially when you have complex requirements that can't easily be accomplished in a simple task or expression. The other day while working on a project I ran across an issue involving a script task and a custom dll, specifically ionic.zip.dll. The script task was failing so I started looking in to the dll. As I was troubleshooting the issue I put together this guide so we could replicate our steps in production. Here is a simple checklist you can follow when working with script tasks and custom dll's in SSIS.

Copy the dll's to your target assemblies directory (depending on your environment, your directory may be different): C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0
Once you copy the dll's, right click and go to properties of each dll and make sure the file is not marked as "blocked". Windows will mark a copied file it thinks is dangerous to run on the machine, like a dll or executable, as blocked. Click Unblock and apply/ok.
Open the Script task in SSIS. Click on the references folder in Solution Explorer. Highlight the dll you are calling. Under reference properties, set the Copy Local option to True.
When working with a custom dll you may need to register it to the GAC (Global Assembly Cache), unless you have a proper installer for it. Open a CMD prompt and navigate to the folder where the gacutil.exe is. Mine could be found here: C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools, though yours might be different. Copy your dll to the folder and register it. Gacutil usage can be found here: https://msdn.microsoft.com/en-us/library/ex0ss12c(v=vs.110).aspx

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Troubleshooting Custom dll’s (ionic) in Script Tasks in SSIS

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