Problem isn't the dependancy on the portal payment settings, the problem is the currency format.
The event module doesn't know how to handle currency formats where the decimal seperator is , instead of . (10,00 instead of 10.00)
The error thrown from paypal is
"The link you have used to enter the PayPal system contains an incorrectly formatted item amount."
The currency per module would be nice but it would even make more sense to do that on event level. (nice enhancement but I would be more satisfied solving the bug)
Cheers,
Thomas