MS Access Query - Data Mismatch Float DataType to nvarchar(100)

Hi Experts,

Currently I am linking a Float DataType to a nvarchar(100) and am getting the error "Data Mismatch)

so I do not link the two tables and create a?:
Convert(varchar(100),[ID])=[UserID3]

ID = Float
UserID3 = nvarchar

But this is not working:
Undefined function 'Convert' in expression
Or it I delete the link:
The SQL Statement could not be executed because it contains ambiguous outer joins

So I tried deleting the link (from one field to the other) and did this:

 IIf(CStr([ID])=[UserId3],[Contact])

Select allOpen in new window

But it runs and runs with a large number of records...

Please help and thanks...