Invitation code is generating ONLY under my CRM user account

Hi all!

I'm using microsoft portal version 8.1. My problem is in generating invitation code.

Only one CRM user can send an invitation. All the other can send an invitation but email comes with empty invitation code. 

In the invitation entity the field is also empty. 

All the users have System Administrator Role in CRM. But the code generates only from one user.

Can somebody tell me what is the problem ?

Thanks in advance!