Yeah, authorize.net will only allow alpha numeric characters for the product name.
One way to get around that would be to use the str_replace function to convert the apostrophe to "´".
find the following code on the confirm page:
$AuthNet_itemized[0][$nextIndex] = "Name";
$AuthNet_itemized[1][$nextIndex] = "".$WA_Store_Cart->DisplayInfo("Name") ."";
and change it to:
$AuthNet_itemized[0][$nextIndex] = "Name";
$AuthNet_itemized[1][$nextIndex] = "".str_replace("'", "´", $WA_Store_Cart->DisplayInfo("Name")) ."";