Assertion `constIdx >= 0' failed in database.h:1358

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What steps will reproduce the problem?
1. I'm running following commands:

$(ALCHEMY_BASE)/bin/learnwts -g -i pre-train.mln -o train-gen.mln -t train.db 
-ne Outcome
$(ALCHEMY_BASE)/bin/learnwts -d -i ore-train.mln -o train-disc.mln -t train.db 
-ne Outcome

With any of the above commands, I get following error and program simply 
terminates with empty output file:

learnwts: ../src/logic/database.h:1358: long long unsigned int 
Database::getIdxOfGndPredValues(const Predicate* const&, const 
Array<Array<std::pair<long long unsigned int, unsigned int> >*>&) const: 
Assertion `constIdx >= 0' failed.


I'm using Ubuntu 14.04.

Original issue reported on code.google.com by girish.i...@gmail.com on 12 Jun 2015 at 8:49