I'd take a look at how you're asking JqGrid to make it's web service call - because it won't know anything about MVC's routing engine by default - and this is all happening client side.
Stepping outside of MVC for a minute, if I have a page:
example.com/page1.aspx
And have a relative link to another page on there:
<a href="page2.aspx">Click here</a>
The browser will look for page2.aspx at the same level as page1.aspx, i.e.
example.com/page2.aspx
If I move page1 to a new folder:
example.com/NewFolder/page1.aspx
The browser will ask for
example.com/NewFolder/page2.aspx
when a user clicks on the link.
The same thing is happening to your GetGridData call - these are being made by the web browser to your server based on the information it has available to it.
So if your page responds on:
example.com/Employee
And asks for a relative request to:
GetGridData
The browser will send that request to the same level that Employee appears to be on:
example.com/GetGriddata
Which then fails because the routing engine can't find a route for that request.
You should look at generating the URL for the GetGridData call dynamically through the routing system, which will ensure that it's built as:
url: "/Employee/GetGridData"
Final edit to add
Forgot to mention, you should probably use the UrlHelper Action methods for this:
url: <%=Url.Action("GetGridData")%>
This will generate a path to the GetGridData method on the current controller. If you need to access a different controller, or pass some values, there are overloads to help.