Can't it be that the issue is in a fact that the user has start access level "No access" in his global user card, comparing to the other user who has "Full access"?

Is the item register only one with which you have issues?

Quick test to do to check is the issue in access rights would be to add as a last row to the access group definition:
Register -> Items -> Full
line...

Best regards,
Eberstein Business Solutions
HansaWorld Business Partner
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Exceeding Customer Expectations
www.ebersteins.com
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