I believe this had been identified as a bug in the Indigo nodes a few weeks ago but it was posted that this has been fixed. Do you have the most recent nightly build of Indigo nodes installed.
Also, try changing the memory policy of the Substructure node to "Write to Disc" to see if this error still occurs.
You can use the pains workflow and the error still occours.
I tried to use other node to do the same but sometimes happen and sometimes no , seems to be an memory error of knime!? as an overflow not resolved ...maybe a clean not fixed.
With the indigo node this error is always present.
Could you try the latest Indigo Nodes version 1.1.2 from the nightly builds repository. We have improved the memory management for the substructure matcher node. If this approach works fine for you then we will do the same for all our nodes.