I got an old project which consist of three different projects. When I am trying to build the project I am getting this error message: 

```
"The type or namespace name 'Ajax' could not be found (are you missing a using    
directive or an assembly reference?)" 

```

I have found solution for missing project or namespace online but it looks like I am missing some default library.

The code looks like this:

```
//Ajax method to Check for existing file name
[Ajax.AjaxMethod()]
public DataTable CheckSearchName(string searchname){
   // code goes here
}

```

Any help?