Windows 7 usb share permissions problem

[tunnel15]

hi
In an all win 7 env ,i have a 1 tb WD external hard drive shared with full rights to Everyone ,Administrators and Users.
All machines were able to access the share but the next day even tho the share shows up
it says you do not have permissions........ on trying to access the share.

All the permissions still show full control even now..

pls help