2007 - Workflow not working

Question

I'm using SharePoint 2007 and I have a really simple workflow that should work on new items in a calendar list:

1) If the author is "MYDOMAIN\user1" or "MYDOMAIN\user2" etc. THEN

2) Set field "Division" as "UserDivision" THEN

3) Pause for 1 minute THEN

4) Send an e-mail to a specified user assigned to the "UserDivision" (the user is "hard coded" in the if block)

Sometimes this workflow works fine, and sometimes it is started and completed (as I can see on the item workflows) but no "Division" field is set and no e-mail is sent. I also checked that is happening with the same user. I mean, sometimes "user1" is correctly assigned to his own division and sometimes not.

ps: this is a little screenshot from SharePoint Designer flow. It's in italian, so please apologize me. (Imposta = set, Invia = send, è uguale a = is equal to, Autore = author, Divisione = division)