[TCL] Script making io freeze.

[JoC]

Hi all!
I am playing around with TCL and I have a problem. I have a script that is run every 5th minute with the ioFTPD sheduler. Problem is that this script sometimes can take 10-15 seconds to execute, and it seems like io freezes until the script is done. Have I done a misstake or is it like this. Can I maybe use some internal timer in the TCL script instead of the sheduler? Any help, code examples or links woul be very much appreciated.