Hotel name: AC Hotel Coslada Aeropuerto
Reserved Rate $55Euro/night
Found rate: $71.87USD/night

According to the Marriott currency converter...
71.87 UNITED STATES OF AMERICA DOLLAR (USD) = 54.98 X EURO EURO (EUR) as of Tuesday, April 23, 2013

Yet I get denied with the following response...

According to our review of your claim, we have determined that the nightly room rate with which your comparison was made is not less expensive than the rate you confirmed via an official Marriott reservation channel.

Can anyone hook me up with a better rate OR give me advice as to what I am doing wrong?

I do see that currency fluctuations are not included in the Marriott LNF guarantee and I'm assuming that the rate is meant to be the same and therefore denied.