With the following client-server JRE/JDK setup scenarios,

S1.
1. both Client and Server were built with JDK1.6.0_29
2. client was running on windows7 with JRE1.7.0_17 64bit, server was running
on Solaris 10 SPARC 64 with JRE1.6.0_29

Result: RMI-IIOP call from client to server was fine.

S2.
Almost the same setup as S1, but change the windows7 JRE to 1.6.0_43 and
1.6.0_29, RMI-IIOP calls were fine.

S3.
Change the windows7 JRE to 1.6.0_45 and 1.7.0_45, RMI-IIOP calls failed.

S4.
1. both Client and Server were built with JDK1.7.0_15
2. client was running on windows7 with JRE1.7.0_45 64bit, server was running
on Solaris 10 SPARC 64 with JRE1.7.0_15

Result: RMI-IIOP calls failed.