Hi
check if any step is worth review and its not already checked.. else ignore as it might be already Implicitly suggested 
1. Check if PI system is stable (as its mentioned that it was restarted)
- RWB-Component monitoring- Cache connectivity Test- All components should be green.
- Do SLDCHECK.
- Check if all app servers are fully up and running . SM51 txn.
- Test by posting a message through RWB , pls observer precaution for production scenario
- Check if all components are registered properly- RWB SLD registration link.
2. Check SOAP UI
- Check the User if its not locked in SU01 Transaction.
- Url is pointing correct, reload the url by generation it again from sender agreement and create a fresh project.
- if you are using channel name in the url , please ensure channel is started and error free status
- Check the Payload you are using , does it has all mandatory header and data fields , use sampler and copy paste the xmls part in order to avoid issues with header.
- check the status of message by switching to status tab in response section , if tis Http 200or HTTP500 .check channel log if there is any entry .
- parameters in soap ui bottom left screen must be filled all the parameters properly , your error details shows its an authorization issue
Regards
Srinivas