Pivot Operator - "potential problem detected: attribute missing" after Select Attributes

Hi all,

according to the pivot operator in my data preparation process RapidMiner is experiencing a 'potential problem':

I have to stream a big amount of data.

In Select Attributes I chose three attributes. One of them named TBLUNIQUELRU_ID is being missed by the pivot operator although it is contained in the Select Attributes output data:

A breakpoint is set after the second operator and I can confirm, that the attribute is contained in the pivot input example set.

Code:

<process expanded="true">
          <operator activated="true" class="jdbc_connectors:stream_database" compatibility="7.2.001" expanded="true" height="68" name="Stream Database" width="90" x="45" y="34">
            <parameter key="connection" value="DB_NAME"/>
            <parameter key="table_name" value="ZZ_RM_TEST"/>
            <parameter key="recreate_index" value="true"/>
          </operator>
          <operator activated="true" breakpoints="after" class="select_attributes" compatibility="7.2.001" expanded="true" height="82" name="Select Attributes" width="90" x="179" y="34">
            <parameter key="attribute_filter_type" value="subset"/>
            <parameter key="attributes" value="|TBLUNIQUELRU_ID|BIT|EVENT"/>
          </operator>
          <operator activated="true" class="pivot" compatibility="7.2.001" expanded="true" height="82" name="Pivot" width="90" x="246" y="187">
            <parameter key="group_attribute" value="TBLUNIQUELRU_ID"/>
            <parameter key="index_attribute" value="BIT"/>
            <parameter key="consider_weights" value="false"/>
            <parameter key="skip_constant_attributes" value="false"/>
          </operator>
          <connect from_op="Stream Database" from_port="output" to_op="Select Attributes" to_port="example set input"/>
          <connect from_op="Select Attributes" from_port="example set output" to_op="Pivot" to_port="example set input"/>
          <connect from_op="Pivot" from_port="example set output" to_port="out 1"/>
          <portSpacing port="source_in 1" spacing="0"/>
          <portSpacing port="sink_out 1" spacing="0"/>
          <portSpacing port="sink_out 2" spacing="0"/>
        </process>

Can someone help?

Ina