weird behavior of mapped drive

Hi, since a few days, I saw a weird behavior of mapped drives on NT Clients. I use a logon script to map some drives letters. The script is working fine but sometimes, the mapped drives just disapear by themselves. I have to run the script agant or map them manually. Another weird thing, I disconnect manually a mapped drive and they reconnect by themselves too after about 10 seconds. If you have some ideas about this kind of problem, tell me.

Thank You