I found a lab case where this error was exactly repeated, included the version of DP and Oracle. UNfortunately, this is where my luck ran out, because the case did not describe an actual resolution
"It would probably be best to check for this thing immediately in GUI and report a warining pop up if capital letters were used when specifying user name"
I found another lab case with the same error, but for Oracle 10 running with DP 6.21
"Install DP Oracle integration agent on each and every node of the Oracle RAC and all the RAC nodes should be in same cell.
Refer "HP Data Protector and Oracle 10g
Suggestions:
G, g, Ag, Hg, LG, Mg, PG, VG, cg, eg, jg, kg, lg, mg, pg, sg
RAC configuration best practices" whitepaper."
This would only be applicable if you are using an Oracle RAC (Real Application Cluster)
You will probably have to open a case to have this problem analyzed