I've made a break through.
Instead of looking at the OS/Oracle setup I decided to have a look at the SQL. After a couple of hours I tracked the problem to the "violation" function in the "rel_constraints" package.
There are two SELECT statements accessing the views rel_contraints_violated_one and rel_constraints_violated_two, both of these cause an EOF on Comms Channel error. This error is also generated by performing a simple SELECT on these views within SQLPLUS.
It looks to me as if there is something wrong with the views but I'll let you know what I find.
