CST waveguide， dont work for >300mm design?

Hi. I′m doing a work about Waveguide slotted 2.4ghz antenna but when i simulate the slotted waveguide (using waveguide port) using a slotted PEC bigger than 300mm, the results are very innacurate (S-dB/farfield/etc), but if the slotted have less than 300mm everything works well. the first issue that i know that something is wrong, is the information about the "number′s processor in use 0", if is <300mm always says 1.
since i dont have CST at home (only in my university)..i have very few time simulation available, if anyone can see the antenna feeding or mesh properties i′ll appreciate.
Thanks.

Hello,
I ran your problem (exactly as you uploaded it), with the waveguide being 475.5 mm long, and I got S11 of about -15.25 db @ 2.45 Ghz. Is that what it's supposed to be?
Regards,
jpsmith123

That′s very close of what i was expecting.. yesterday when i did the simulation (using that uploaded file), the S1,1 between 2ghz and 3ghz was always between -8.65 and -8.68, obviously something was wrong.
Maybe the CST installation in my university is corrupted..i dont know.
Can you upload the file with the results? i appreciate a lot, to explain at my university that something is wrong..
Thanks.

I'll send it to you by way of PM.
Regards,
jpsmith123

If you're using CST2006-version, you need install the last Service Pack from CST company.

Use Agilent EMDS for such problems.

yes..with the latest Service Pack works just fine.
Thanks.