If you are attending one of CASSS's events outside the USA, you might be able to claim back the VAT/GST paid out on registration fees and other related costs. In general, individuals can't claim back this sales taxes, but companies can in some cases recover them.
Contact CTAX to find out your company qualifies for a VAT/GST refund. You will need the VAT/GST invoice(s) associated with these charges.
Please pass this information on to your accounting department.