You do not have permission to access [drive]. Contact your network administrator to request access

For example: "You do not have permission to access \\my-pc\k. Contact your network administrator to request access"

When this error results from trying to access a PC's shared drive (not just a sub-directory but the entire shared drive) from another client PC on a (wireless) network, it could be that in addition to setting sharing permissions on the drive share, you have to remember to also set security access permissions for the drive itself :

• Right-click on the drive, 
• Click properties,
• On the 'Security' tab (NOT 'Sharing' tab), click Edit,
• On Security dialogue, click Add,
• Type Everyone (click Check Names) and click OK,
• Apply the necessary permissions (like Full Control, Read, Modify, etc),
• Click OK (2x)