Method:1

• Type gpedit.msc in RUN dialog box.
• Group Policy Window will be opened.
• Goto : User Configuration -> Administrative Templates -> System
• in right-side pane, set “Prevent access to Registry editing tools” to either Not Configured or Disabled.

Method:2

• Press Windows Key +’R’
• Type the following and hit Enter

REG add HKCUSoftwareMicrosoftWindowsCurrentVersionPoliciesSystem /v DisableRegistryTools /t REG_DWORD /d 0 /f

Method:3

Alternatively, Copy the following code,paste in any notepad and save as “EnableRegEdit.inf”

   [Version]
Signature="$Chicago$"  
Provider=Symantec  
[DefaultInstall]
AddReg=UnhookRegKey  
[UnhookRegKey]
HKLM, SoftwareCLASSESbatfileshellopencommand,,,"""%1"" %*"  
HKLM, SoftwareCLASSEScomfileshellopencommand,,,"""%1"" %*"  
HKLM, SoftwareCLASSESexefileshellopencommand,,,"""%1"" %*"  
HKLM, SoftwareCLASSESpiffileshellopencommand,,,"""%1"" %*"  
HKLM, SoftwareCLASSESregfileshellopencommand,,,"regedit.exe ""%1"""  
HKLM, SoftwareCLASSESscrfileshellopencommand,,,"""%1"" %*"  
HKCU, SoftwareMicrosoftWindowsCurrentVersionPoliciesSystem,DisableRegistryTools,0x00000020,0  

Right click it and choose ‘Install’ to solve the problem.