BigInteger not invertible

[diranl]

Sporadic error message occurring when PET decommitments are computed.

To note: Decommitments are performing divisions.

Error Log:
Exception in thread "main" java.lang.ArithmeticException: BigInteger not invertible.
at java.math.MutableBigInteger.modInverse(MutableBigInteger.java:1329)
at java.math.MutableBigInteger.mutableModInverse(MutableBigInteger.java:1205)
at java.math.BigInteger.modInverse(BigInteger.java:2014)
at civitas.util.CivitasBigInteger.modDivide(CivitasBigInteger.java:162)
at civitas.crypto.concrete.PETShareC.decommitment(PETShareC.java:64)
at secureprinting.mixnet.TranslationTable.extract(TranslationTable.java:131)
at secureprinting.mixnet.TranslationTable.extract(TranslationTable.java:156)
at secureprinting.Controller.main(Controller.java:60)