I'm still on Build 5140 so the ePO integration in B5300 may have changed this but here goes nothing... First confirm the SafeBoot Database Server service is started in services.msc? If it's not listed in Services or it's not started then run the SafeBoot Database Server, login and choose Start Service from the menu.
If this doesn't help check SDMCFG.INI in C:\Program Files\SafeBoot\ on the client and confirm the following values are correct. [Databases] Database#=[a_valid_ip_address] [Database#] Description=[YOUR_SAFEBOOT_DB_DESC] IsLocal=No Authenticate=No Port=5555 ServerKey=[Some very long string] AuthType=1
Your INI may hold multiple database sections. Confirm you can ping the IP(s) listed in the config file from the client machine. If the only Database# value is SBFILEDB.DLL then you're client config is incorrect.
do you have the service running? Go to the server, go to start, programs, safeboot, and select safeboot server. Go the the top option, i believe under the file options, and make sure you have selected to run as service. This error means that the service is not open for requests.