0x800a1391 - JavaScript runtime error: 'Page_ClientValidate' is undefined

So ive used this exact button on other forms without an issue...Today it is
<asp:Button ID="btnSubmit" runat="server" Text="Submit Form" UseSubmitBehavior="false" OnClientClick="this.value = 'Please wait...'; if(Page_ClientValidate()) { this.disabled = true; } else {this.value = 'Submit Form'; return false;}" Style="margin-left: 55px" Height="27px" Width="114px" OnClick="btnSubmit_Click1"></asp:Button> So on button click i get thi error......
Unhandeled exception at line 176...blah, blah
0x800a1391 - JavaScript runtime error: 'Page_ClientValidate' is undefined and it changes the button caode to this
<input type="button" name="ctl00$MainContent$btnSubmit" value="Submit Form" onclick="this.value = &#39;Please wait...&#39;; if(Page_ClientValidate ...