DevOps, CI/CD and Automation

My PHP variable definition looks like:-
$StartDate="2006/01/01 06:00:00";
$EndDate="2007/07/26 17:00:00";

the stored procedure I am trying to use contains

PROCEDURE spTablesPlayed(
p_number cards.card_number%type, --varchar2
p_startdate varchar2,
p_enddate varchar2,
cv_tablesplayed out tablesplayed_cur_type);

and I get the following error

Warning: ocibindbyname() [function.ocibindbyname]: OCIBindByName: ORA-01036: illegal variable name/number in C:\Program Files\Apache Group\Apache2\htdocs\Events\OracleGetClientTest.php on line 111

at my line

OCIBindByName($stmt,":p_startdate",&$StartDate, 20);

Please tell me what I have misunderstood/misdefined.