\\computername\ is not accessible. you might not have permission to use this resource

---- 1st solution ----

When you can not access folder, please follow .
1- Right click My Computer->Manage->Local User and groups->User->ple see user Guest and right click then properties->UnKick accound is Disable.( i mean that u unkick this guest accound is enable.)
2-start->sitting->Controlpanel->Administrative Tools->Local security policy->Local Policies->user Rights Assignmen->duble Click Deny access to this computer from the Network and then remove all list that it have(Like Guest,support_.....)

---- 2nd Solution ----

This lack of a user password has caused problems in the past with Task Scheduler not working correctly and I have modified the Registry under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa to change limitblankpassworduse to "0" instead of "1" to make the scheduler work correctly.

I purchased a new terabyte external hard drive that was pre-formatted as an NTFS single partition to use as a backup drive using Norton Ghost.

I regularly have shared the hard drive on one of my computers with the other two, so I am familiar with sharing and Security rights.

When the new drive was added to the main computer either as a USB attached drive or as an eSATA connection, I could read and write to the drive from the main computer. However, when I marked it as a shared drive with full rights to others, I could see it from my remote networked computer but when accessed I would get the message: " is not accessible. You might not have permission to use this network resource"

I have tried many suggestions from the web including the ones from Microsoft support. They include:
Regedit and set limitblankpasswords to zero
Regedit and set restrictanonymous to zero
be sure that the Guest account is activated
be sure that permissions are granted for the folder
share the drive as well as the folder (you are not allowed to set permissions settings on the drive)
disable simple file sharing
disable the firewall
add a password for yourself on both machines because anonymous users cannot access a shared drive.

None of these proposals along with several others that I tried ever worked.

However, I stumbled across a Security change that did work:
1. From Control Panel choose Administrative Tools> Computer Management> Storage> Disk Management
2. Right click on the drive in question
3. Choose Properties and click the Security tab
4. Click the Everyone User Group and notice that the Permissions for Administrators boxes are not checked.
5. Click on the Allow> Full Control box and then the Apply button at the bottom.
6. You can check the other users and groups in this window and allow them full use also.
7. Click OK and exit the Security window.
8. You now should be allowed access to the drive via sharing on the Workgroup network.