Do feel too bad, I had the same problem with a 510 Aerohead on my 13ft 7/8. I cast a A/F 480 scandi and a N/C FF70 8/9 without issue. For some reason I just couldn't make the Aerohead work on my rod. I can also use a Rio
Long Sead Spey and it's at the limit but works well.
The only thing I could figure is that something about the taper/design just didn't like my casting style/set up. I put a couple hours into trying to make it go and was only successful about 10% of the time. I finally went back to what works for me.