Q:

Error converting data type nvarchar to bigint -when joining two differnet data types

I am trying to join two tables.  
Table1.Column1  where column 1 is a BIGInt. 
On
Table2.Column2 where column 2 is Nvarchar.  
Here is what I am running 
Select HspId, CMSid, Cast(CMSId as nvarchar)
From Q2IMSSiteHistory2015old
inner Join HSP on HSP.CMSid = Q2IMSSiteHistory2015old.POS

I am getting the following Error: Error converting data type nvarchar to bigint.
Even if I do not cast anything I get the same error.  

A:

Cast the join.
Select HspId, CMSid, Cast(CMSId as nvarchar)
From Q2IMSSiteHistory2015old
inner Join HSP on CAST(HSP.CMSid as nvarchar) = Q2IMSSiteHistory2015old.POS

