You must show us your schematic. The easiest way is to use two equal value resistors directly across the 0-10V signal. At their center it will be 0-5V and no op-amp is needed.
This scheme have 1.5 gain not 0.5. Anyway, for scaling voltage by 0.5, as was mentioned, it's much easy to use a voltage divider. For what reason you choose an OP AMP?
IF the DC conditions were correct it would give a gain of 1.5.
What you want is an attenuation of 2 times (= gain 0.5). If you want to use an op-amp, connect two 10K resistors in series across the input and ground and from their junction connect the op-amp as a unity gain buffer. Connect the input to the + amp input and link the - input directly to the output pin.