Error in using .NETLink in Mathematica to invoke Matlab

I used before following code to call MATLAB from MATHEMATICA without any problem

In[1]:= Needs["NETLink`"]
matlab = CreateCOMObject["matlab.application"]

But now i have an error like this:

CreateCOMObject::netexcptn: "A .NET exception occurred: !(TraditionalForm`\"System.Runtime.InteropServices.COMException (0x800401F3): Invalid class string (Exception from HRESULT: 0x800401F3 (CO_E_CLASSSTRING))\\n at System.RuntimeType.GetTypeFromProgIDImpl(String progID, String server, Boolean throwOnError)\\n at Wolfram.NETLink.Internal.COM.COMUtilities.createCOMObject(String clsIDOrProgID)\\n at Wolfram.NETLink.Internal.CallPacketHandler.createCOM(KernelLinkImpl ml)\")."

I installed .net framework 4 on Win 7 x64. Is it a .Net framework error?

It was solved by reinstalling MATLAB.