Problem with 7.4 driver

I just upgraded to 7.4 and I'm getting this when I try to use the jdbc
driver:

Exception in thread "main" java.lang.NoSuchMethodError:
org.postgresql.core.StartupPacket.writeTo(Lorg/postgresql/core/PGStream;)V
at
org.postgresql.jdbc1.AbstractJdbc1Connection.openConnectionV2(AbstractJdbc1Connection.java:585)
at
org.postgresql.jdbc1.AbstractJdbc1Connection.openConnection(AbstractJdbc1Connection.java:215)
at org.postgresql.Driver.connect(Driver.java:122)
at java.sql.DriverManager.getConnection(DriverManager.java:512)
at java.sql.DriverManager.getConnection(DriverManager.java:171)

But I checked and that method does indeed exist. I built the driver
twice. Any idea what the problem is?

The line that throws the Error is:

new StartupPacket(PGProtocolVersionMajor,
PGProtocolVersionMinor,
PG_USER,
database).writeTo(pgStream);