Few common errors in BPEL of Oracle SOA suite are:
1. No domain available for the current user
This occurs due to failure to contact Olite database instance while loading SOA suite in the system. As this db has the all meta info regarding the domain names etc. within the server.
You need to run Olite database bat files for this.
Generally the path to these files would be
D:product10.1.3.1OracleAS_2bpelinstallbin
These are bat files and file names contains olite string. ex: reg_olite.bat
These names and paths might change based on the version of SOA suite. This configuration exists for 10.1.3.1