Error R6030 loading our program

We are a software house in Italy. We have updated our software to some customers. With some PCs (Xp, Vista and Win7) where is installed Norton360, our program crash on load for a runtime error R6030 crt not initialized.
Disabling the antivirus does not resolve the problem. Only the removal of the Norton Service allows our program to start. I made a virtual machine Xp where I can reproduce the problem. The italy assistance has tried to solve the problem but not results.
Please note the this issue is very urgent.
Thanks