how to solve script error

my code

  Response.Write("<script>alert('Please enter City/Keyword for Search');</script>");

Error:
Microsoft JScript runtime error: Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled.
Details: Error parsing near '<script>alert('Please enter City/Keyword for Search');</script>.
how to solve this

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