Opening linked SYNCHRO .spx file after upgrading from Pro 6.3.2.0 to 4D Pro 6.4.3.2

Hi, 

as a channel partner received this question about Synchro: 

Opening a Synchro file with a linked SYNCHRO .spx file after upgrading the desktop application from Pro 6.3.2.0 to 4D Pro 6.4.3.2 creates a warning; how can this be solved? (Should the linked file be upgraded separately by opening it individual?) 

Please advise (or confirm), so this experience can be shared,

Thanks,

Joost