ORA-1830: date format picture ends before converting entire input string

I am trying to create a new OraceTimeStampTZ object and I get the above error and can't see why. When I examine the string passed to "new", it looks OK:

OracleTimeStampTZ dtzTimeIn = new OracleTimeStampTZ(sDTZ);

sDTZ = "15-APR-13 09.03.47.000000 AM US/EASTERN"