Prepared Statements with ruby pg gem

I am trying to use the prepared statements in ruby with pg gem. This is
how my statement looks like

conn.prepare(“insert_values”, "insert into " + objectName + “(” +
headerStr + “) values (” + prep_values + “)”)
conn.exec_prepared(“insert_values”, arr)
I keep getting the error

Prepared Statement insert_values already exists.

How Do i Fix this?? Thanks