Mysql exception,

Mysql error. URGENT! Warning: mysql_fetch_assoc () expectsparameter1toberesource, booleangiveninD: \ wamp1 \ www \ empmanage \ empMain. phponlin mysql error, urgent!
Warning: mysql_fetch_assoc () expects parameter 1 to be resource, boolean given in D: \ wamp1 \ www \ empmanage \ empMain. php on line 37

The code is as follows:
$ SQL = "select * from emp limit". ($ pageNow-1) * $ pageSize. ", $ pageSize ";
$ Res2 = mysql_query ($ SQL, $ conn );
37 rows while ($ row = mysql_fetch_assoc ($ res2 )){
Echo "{$ row ['id']} {$ row ['name']} {$ row ['Grad']}".
"{$ Row ['email ']} {$ row ['salary']}".
"Deleting users and modifying users ";
}
Echo "";
Explain the reason for this sentence.

------ Solution --------------------
It indicates that 36 returns the value of boolen's false instead of resource.
Change row 36 to $ res2 = mysql_query ($ SQL, $ conn) or die (mysql_error ());
What is output?