Any idea of this issue

For normal exception create a general function which logs any exception into the database like 

public void LogException(Exception ex)
{
//Store ex.Message / ex.StackTrace and whatever else into database 
}

Now from catch block call this function to log.

catch(Exception ex)
 LogException(ex);

You can also check the Type of exception inside LogException function to log specific values for an exception.

It's likely that the PostSharp is a good choice,use attribute to log exceptions

You needed to handle this from the start, it's a bit late now. You're going to have to go back and change all your methods to call your database method. That's not so hard to do, a global search and replace would do it, replace

catch(Exception e)

{

with

catch(Exception e)

{

     DataLayer.LogException(e);

See my code.catch (Exception EXApplication) { ExceptionHandler.Publish(EXApplication); } Where ExceptionHandler.Publish is my library function to log error in database

Like others have suggested, I suggest you just bite the bullet and do a find and replace. Note that Visual Studio has support for regular expression searches, so you can find any catch block (no matter the exception caught). However, if you really want to look into this further, you might be able to use runtime code generation and reflection to find catch blocks then inject code into them at runtime. Here's an article to get you started (although I strongly advise against going down this path, as it could get quite complex and may not yield results): .Net Code Injection. Here is a CP article on Reflection.Emit(): Article.

ok but i am really stuck into this issue,

i know i can add a global error hangling like

Application.ThreadException += new System.Threading.ThreadExceptionEventHandler(Application_ThreadException);

but this will only works for unhandled excetions but what about handled exceptions how to add new event handlers

this will work if you have a small amount of try catch blocks but in my case doing this will take alot of time

any others suggestions