Resolution:
On some 64-bit OS, for BW, during runtime, the loaded 'jar' files are in NOT in the order required by BW engine.
For example, in AIX 5.3 64-bit OS, for BW, it loads the RV 'native jar' files first instead of 'tibrvj.jar'. This results in the above error.
- Issue faced using TRA 5.5, BW 5.4 on AIX 5.3 64-bit system.

Solution:
1. move tibco/bw/5.3/bin/bwengine to tibco/bw/5.3/bin/bwengine32
  - copy tibco/tra/5.5/bin/wrap64 to tibco/bw/5.3/bin/bwengine
2. in the deployed bw engine tra file, for tibco.env.STD_EXT_CP, replace  
%RV_HOME%lib
with
%RV_HOME%lib/tibrvj.jar

Also note: this solution is applicable for any 64-bit OS where BW reports this error