what is the underlying technology of your partner service? it looks like it is returning a bad soap/http response. apparently the status header has some bogus "-***" characters appended to it.
by the way, the trace you show corresponds to an error in the web services stack of jboss as, not directly related to jbpm bpel.
on a different thought, does a similar error show up when you try your process under jboss 4.0.4 or above?