Round Robin Rule is not working

Round Robin Rule is not working

I am stuck and dont know whats wrong... 

I have 2 Round Robin rules but only one is working....

The first Rule should assign Tickets to the "Pre Sales" Team, if "Account Number" (custom field) is empty.

I "thought" that if i would make the Account Number field mandatory in the portal Ticket submit form, that all tickets which are created via portal will have the Account number. Therefore i can easily assign them to the Account-Team via round robin. 
Other tickets which are automatically created via incoming E-Mails wont have an account number and are should be assigned to the Presales Team via the round robin rule which is not working.....

The second Round robin rule assignes tickets to avaiable agents. This rule is working absolutely fine but its the only one which works.... 
So what do i have to change to make the first Round Robin rule working correct??