if string conditional

[bekti]

Code:

<setvar r>array('{string1}', '{string2}', '{string3}')</setvar> <?=$GLOBALS['tplvars']['r'][array_rand($GLOBALS['tplvars']['r'])?>

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but when i try to set

Code:

<setvar r>array('{myadvertisements[zone_1]}', '{myadvertisements[zone_2]}', '{myadvertisements[zone_3]}')</setvar> <?=$GLOBALS['tplvars']['r'][array_rand($GLOBALS['tplvars']['r'])?>

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it's appear an error..my header template doesn't show up...

any fix?