problem using webdav

Hi,
 
i am using webdav to access resources on server. i am using apache
tomcat server's  webdav project for testing webdav. i open a file from
server , edit it . when i save it through IE(using save as open and
giving full URL on server) it says that file is readonly . if i save it
from diferent name it is saved . how to solve this issue ..........
please help................
 
 
thanks and regards
Geeta