While I was writing an in-line code with javascript inside the master page I was constantly facing the following exception.

The Controls collection cannot be modified because the control contains code blocks (i.e. <% … %>).

Welcome, <script type=”text/javascript”>var loginName = “<%= SPContext.Current.Web.CurrentUser.Name %>”;document.write(loginName);</script>

Found out that the javascript with c# code needs to be out of the tag which has runat=”server”. After checking the code I re-wrote the code into 2 pieces

<script type=”text/javascript”>var loginName = “<%= Microsoft.SharePoint.SPContext.Current.Web.CurrentUser.Name %>”;</script>

The above code I moved out of the “<form runat=”server”…” code and the below code inside the required location.

<span>Welcome, <script type=”text/javascript”>document.write(loginName);</script></span>

Now the page is rendered properly.