Arduino and RFID-reader in Flash: slow movie

I am using Flash for controlling an Arduino and RFIDreader. A movie should start playing when a specific tag is scanned. The Arduino is used for the input values of a distance sensor and activating some LED's.

The problem is: after a while the movie will play very slowly and the sound will be distorted. When the program just starts running there is no problem, but after a couple of minutes it will do this.

I am using serproxy to make Flash communicate with my Arduino.

Does anybody know if there is a way to solve this problem or should I consider start working in a different program?