You have to use following steps to fix this problem.
1.First you have to change the NTLM authentication level. You can find ths in the following link:
Network security: LAN Manager authentication level
2.Now for changing the policy, go to start button -> now go to the search option -> now type "gpedit.msc" and press ok. If you get this, then open it and locate to:
3.Now change the value to “Send LM & NTLM - use NTLMv2 session security if negotiated”.
Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options\Network security: LAN Manager authentication level