I've had SBR's and suppressors for several years now, and sometimes travel to IA to visit family.
I know suppressors are illegal there, but in the past I have applied for, and gotten approval to transport
a couple SBR's into IA to shoot etc. All of a sudden, this years application (ATF 5320.20) was disapproved
with the reason given; "State Law Prohibits".  Has the law recently changed, now forbidding them
or have my previous approves been a mistake on the ATF's part?

Using my parents Sioux City, IA address as the destination if that makes a difference.

Thanks,
Ray

Law hasn't changed.  State law does prohibit SBRs,  I think the ATF made a mistake.

I'd say the previous approvals were in error.  Lucky you didn't get stopped/checked.