This is a symptom specifically when compiling an Excel VBA project. The following error occurs:
User-defined type not defin
For the Scripting.Dictionary type, you can either use late binding (as already pointed out ) with:
Dim Dict as Object
Set Dict = CreateObject("Scripting.Dictionary")
Which works, but you don't get the code auto completion. Or you use early binding, but you need to make sure that VBA can find the Scripting.Dictionary type by adding the reference to the Microsoft Scripting Library via VBA-->Tools-->References--> "Microsoft Scripting Runtime". Then you can use:
Dim Dict as Scripting.Dictionary
Set Dict = New Scripting.Dictionary
... and auto completion will work.