Falsh meter + 580 EX II + ste 2 = problem

Today i was testing a setting with an umbrella, ste 2 and 580 EX II + eos 30D. All in manual mode.

When i try to use the flash meter ( sekonic) in a dark place ( not so dark, but dark), the flash meter give me a EU ( error reading). I use the sekonic without a syncro wires , on auto detec position.

After some test it appears that is one of the red lignt on ste2 or flash that give a sgnal bright enough to be detectable by the flash meter.

Can i tape one of the red light on the ste2 or flash.

What do you suggest ?

Thank you