MicroSoft Jscript runtime error:Sys.webforms.pagerequestmanager server error exception:

Question

MicroSoft Jscript runtime error:Sys.webforms.pagerequestmanager server error exception:An unknown error occured while processing the request on the server.the status code returned from the server was 404.

MicroSoft Jscript runtime error:sys is undefined,type undefined,object null.

i got above earrors when i am clicking submit button and update button and cancle button.i dont know how to resolve it .plese help me any one about this issue.i am using asp.net 4.0,updatepanal and scriptmanager,and editor control.