i2b2 Gotchas Concept Code in Query not in Quotes
This is caused by the c_columndatatype of concept in the ontology table in the meta databse being an 'N' as opposed to a 'T'.
The documentation says that this is the value 'describes the datatype of the concept'. It doesn't. It describes the datatype of the concept code or, probably more correctly in this case, the concept path. Hence if it is a number, no quotes required.