Cant convert list element STRING to LONG

Cant convert list element STRING to LONG

htmlpage Recorrido_Attn(okID, Soc)

<%{%>

<link href="l1t1c2sda.css" rel="stylesheet" type="text/css" />

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<%okList = input.okID.toList();

    for each l in okList

    {

        StL = l.toString();

        StL2 = StL.getAlphaNumeric();

        StL3 = StL2.removeAllAlpha();

        StL4 = StL3.trim();

        StL5 = StL4.toLong();

%>

 <%=StL5%>                                          <%}%>

<%}%>

Error details: Error occured while executing the script. Unable to update variable StL5 Invalid Numeric Format found Cannot convert the String to Numeric