Get( AccountName )= "Technician::UserName"
compares the current AccountName such as "Fred" to the literal text "Technician::UserName" instead of the text stored in the username field. So you need to remove the quotes for start. Also, this script assumes that you are automatically on the correct record for "Fred". You might have a dozen records, one for each user and this If test will not return true unless the current record happens to have the matching data.
If the if step does not return True, you don't go to the layout for Technician and this may keep Insert Calculated from putting any value in your field, which will produce the error message you report.
I think you need this script:
Go to Layout ["Technician"]
Enter Find Mode
Set Field [Technician::UserName ; Get ( AccountName ) ]
(I used set field instead of Insert calculated. Insert steps require that the field receiveing the inserted data be physically present on the current layout. Set field steps do not have this limitation.)
Thank you it worked perfectly