No access for users after migration from US to EU dc on CRM

No access for users after migration from US to EU dc on CRM

Hi all,

I recently transferred our Zoho CRM from the US to EU data center by exporting everything and then re-importing all my events, leads etc. 
Everything works fine but my team mate is unable to access this new CRM while he has an EU account set up correctly.

I de/re-activated his user but didn't help. 
Also deleted him from Zoho CRM and recreated a new one but it doesn't help.

Can anybody provide me with an alternative? 
I'd rather not ask him to delete his account and create a new one!

Thanks in advance!
Adrien