Are you receiving error messages similar to  \"Error 40: could not open a connection to SQL Server\", these types of errors generally occurs with SQL Server 2005, because default settings SQL server, does not allow remote connection and generate error 40 while establishing the connection with SQL server, and it leads to certain unexpected error due to which the system performance degrades. With the help of given solution you will be able to clean the system errors and run your PC normally.

You can also fix error 40 yourself but it require manual effort. Firstly, try to correct the registry if you are able to do so, because you may also corrupt your operating system if you will change the unnecessary value of registry, follow these steps to do registry settings in order to correct registry value,  goto “LocalAccountTokenFilterPolicy”  under windows,  it is an important file which run the operating system smoothly. However, this file sometime get damage or corrupt while installation and un-installation of program or application, If you want to fix error 40 perform the steps below:

• Type “Regedit” in the run and press “Enter”.
• A dialog box will open, named Registry Console, click “HKEY_LOCAL_MACHINE” and expend SOFTWARE-Microsoft; and click Windows-CurrentVersion
• Now goto Policies and explore the given path HKEY_LOCAL_MACHINE-SOFTWARE-Microsoft-Windows-CurrentVersion-Policies-System.
• Find “LocalAccountTokenFilterPolicy” in the registry key, if you have not find the value then perform the below step to add its value.
• Click on New in the Edit menu and select DWORD Value command.
• Then Type “LocalAccountTokenFilterPolicy” and Click OK.
• Now Modify the value of “LocalAccountTokenFilterPolicy” to 1 in value data and click OK.
• Close the dialog box and reboot your PC.

It is a very time consuming task, and there is also chance of corruption of your OS, so it is better to  use a registry clean tool to fix error 40.

Disk De-fragmentation is also a process with the help of which you can maintain the health of PC, it is  necessary to remove the file cluttered from hard disk because thousand of file located on the hard disk and they get disorder and consume unnecessary space when you install or un-install any application. So, it is also helpful to reduce the negative aspects of error 40. Launch Disk De-fragment by right clicking on the particular drive, select properties, and choose De-fragment.

Virus infection also causes to the error 40, because error 40 main causes is the corruption of file and registry value, which directly or indirectly effect the files system of operating system or any application which causes to errors 40 in your PC.

Hope you will be able to resolve the problems caused by error 40, this article will help you to find the root causes of error 40 and the solution to the same.