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

I have an ASP.NET webform with some controls and when I press the submit button, I get the following error

sys.webforms.pagerequestmanagerservererrorexception: Price can not be zero. Parameter Name: url

When I submit the button I am putting values ​​in the database.

How can I fix this problem?

When I try putting a breakpoint on the page load, no symbols have been loaded for this document.

The HTML for the submit button is shown below

  & lt; Input type = "submit" Name = "ctl00 $ ContentPlaceHolder1 $ btn submit" value = "submit" onclick = "javascript: WebForm_DoPostBackWithOptions (new WebForm_PostBackOptions (& quot; ctl00 $ ContentPlaceHolder1 $ btnSubmit & amp; quot ;, & amp; "Id =" ctl00_ContentPlaceHolder1_btnSubmit "/>  
   / Pre> 
 Please 
 

  & lt; Input type = "submit" name = "ctl00 $ content placeholder 1 $ submit $ btn" value = "submit" onclick = "btnSubmit_Click" OnClientClick = "btnSubmit_Click" id = "ctl00_ContentPlaceHolder1_btnSubmit" />