Value cannot be null. Parameter name URL on ASP.net form submit

Question

Hello,

I have a ASP.net webform with few controls and when I hit the submit button I am getting the following error

sys.webforms.pagerequestmanagerservererrorexception: Value cannot be null. Parameter name:url

On submit of the button I am just inserting values into the database.

How do I fix this issue?

When I try to put a breakpoint on page load it says No symbols have been loaded for this document.

HTML for the submit button is shown below

<input type="submit" name="ctl00$ContentPlaceHolder1$btnSubmit" value="Submit" onclick="javascript:WebForm_DoPostBackWithOptions(new WebForm_PostBackOptions(&quot;ctl00$ContentPlaceHolder1$btnSubmit&quot;, &quot;&quot;, true, &quot;&quot;, &quot;&quot;, false, false))" id="ctl00_ContentPlaceHolder1_btnSubmit" />

Please help