jsonRPCClient Error with php variables

I am trying to run the following code

$betamount=$_POST['bet']; 
$litecoin->move($myusername,Admin,$betamount);

but it will not work. it does however work when i replace $betamount with an actual number ie

$litecoin->move($myusername,Admin,0.2);

or

$betamount=0.1; 
$litecoin->move($myusername,Admin,$betamount);

any ideas on whats going wrong ? the $_POST[‘bet’] is defiantly a number because i have tried multiplying in php and it all works fine.