Inner join across an instance

I am currently trying to inner join between two databases.  One of them is a true database, and the other is an instance.  While I can pull records from one without a hitch (they have been linked), when I try to perform the join, I'm told that it cannot find the column in question.  Here's the statement I've been trying:

SELECT equipmentId
FROM [CHSQL01\ABOUTTIME].[abtt].[dbo].[Equipment]
INNER JOIN VPTest.dbo.bEMEM
ON [CHSQL01\ABOUTTIME].[abtt].[dbo].[Equipment].[equipmentCode] = VPTest.dbo.bEMEM.Equipment

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And this is the error, I'm receiving:

Msg 4104, Level 16, State 1, Line 4
The multi-part identifier "CHSQL01\ABOUTTIME.abtt.dbo.Equipment.equipmentCode" could not be bound.

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Any help is greatly appreciated.  Thanks in advance!