subprocess error when tech pref gives same value at a certain time step

inputfile_subprocesserror

<simulation>
  <archetypes>
    <spec>
      <lib>agents</lib>
      <name>NullRegion</name>
    </spec>
    <spec>
      <lib>cycamore</lib>
      <name>Source</name>
    </spec>
    <spec>
      <lib>cycamore</lib>
      <name>Reactor</name>
    </spec>
    <spec>
      <lib>cycamore</lib>
      <name>Sink</name>
    </spec>
    <spec>
      <lib>d3ploy.timeseries_inst</lib>
      <name>TimeSeriesInst</name>
    </spec>
  </archetypes>
  <control>
    <duration>50</duration>
    <startmonth>1</startmonth>
    <startyear>2000</startyear>
  </control>
  <facility>
    <config>
      <Source>
        <outcommod>fuel</outcommod>
        <outrecipe>fresh_uox</outrecipe>
        <throughput>1</throughput>
      </Source>
    </config>
    <name>source</name>
  </facility>
  <facility>
    <config>
      <Sink>
        <in_commods>
          <val>spent_uox</val>
        </in_commods>
        <max_inv_size>10</max_inv_size>
      </Sink>
    </config>
    <name>sink</name>
  </facility>
  <facility>
    <config>
      <Reactor>
        <assem_size>1</assem_size>
        <cycle_time>1</cycle_time>
        <fuel_incommods>
          <val>fuel</val>
        </fuel_incommods>
        <fuel_inrecipes>
          <val>fresh_uox</val>
        </fuel_inrecipes>
        <fuel_outcommods>
          <val>spent_uox</val>
        </fuel_outcommods>
        <fuel_outrecipes>
          <val>spent_uox</val>
        </fuel_outrecipes>
        <n_assem_batch>1</n_assem_batch>
        <n_assem_core>1</n_assem_core>
        <power_cap>1</power_cap>
        <refuel_time>0</refuel_time>
      </Reactor>
    </config>
    <name>reactor1</name>
  </facility>
  <facility>
  <config>
    <Reactor>
      <assem_size>1</assem_size>
      <cycle_time>1</cycle_time>
      <fuel_incommods>
        <val>fuel</val>
      </fuel_incommods>
      <fuel_inrecipes>
        <val>fresh_uox</val>
      </fuel_inrecipes>
      <fuel_outcommods>
        <val>spent_uox</val>
      </fuel_outcommods>
      <fuel_outrecipes>
        <val>spent_uox</val>
      </fuel_outrecipes>
      <n_assem_batch>1</n_assem_batch>
      <n_assem_core>1</n_assem_core>
      <power_cap>1</power_cap>
      <refuel_time>0</refuel_time>
    </Reactor>
  </config>
  <name>reactor2</name>
</facility>
  <recipe>
    <basis>mass</basis>
    <name>fresh_uox</name>
    <nuclide>
      <comp>0.711</comp>
      <id>U235</id>
    </nuclide>
    <nuclide>
      <comp>99.289</comp>
      <id>U238</id>
    </nuclide>
  </recipe>
  <recipe>
    <basis>mass</basis>
    <name>spent_uox</name>
    <nuclide>
      <comp>50</comp>
      <id>Kr85</id>
    </nuclide>
    <nuclide>
      <comp>50</comp>
      <id>Cs137</id>
    </nuclide>
  </recipe>
  <region>
    <config>
      <NullRegion>
      </NullRegion>
    </config>
    <institution>
      <config>
        <TimeSeriesInst>
          <calc_method>poly</calc_method>
          <record>1</record>
	  <demand_std_dev>0.0</demand_std_dev>
          <demand_eq>3*t</demand_eq>
          <commodities>
              <val>POWER_reactor1_1_t</val>
              <val>POWER_reactor2_1_3*t</val>
              <val>fuel_source_1</val>
          </commodities>
          <steps>1</steps>
        </TimeSeriesInst>
      </config>
    <name>source_inst</name>
    </institution>
    <name>SingleRegion</name>
  </region>

</simulation>