Does this flashing error appear on the Handheld device or on the RailMaster PC?
If error displays on the Handheld device, is there any additional indication of something wrong showing on the RailMaster PC?
EDIT: After Googling "ERROR: Object Event". It might have something to do with a failure in TCP/IP handshaking between your handheld device and the RailMaster PC. Possibly loss of IP address matched subnet values. The RailMaster PC needs to be configured with a 'static IP address'. If you don't do this, then the default DHCP [Dynamic Host Control Protocol] can occasionally assign a new different IP address to your RailMaster PC. As this address is manually configured in the 'Handheld' device. If DHCP changes the RailMaster PC IP address, then the IP connection is lost.
This previous thread gives details and documents the IP address configurations options. The information in this existing thread might assist with your issue. Look at the ADDENDUM post - 4th one down on the page.
If the linked thread above offers no assistance. Then report your issue observations to HRMS [Hornby RailMaster Support] using the integral 'reporting function' located in the RailMaster 'Help Screen'.
Some other things you can try.
If this error has only just appeared during this particular play session, then power down all your kit including the handhelds and reboot everything afresh.
If this error has been visible over several power-ups and shows on the PC, then it might be a missing / corrupted RailMaster DLL file [as some Google search results indicate as being a possible cause]. In which case, even if your installed RailMaster version is already 1.73 then download the current RailMaster installer file from the download link at the top of the RailMaster forum. Right click the installer file and choose 'Run as administrator'. Do not have RailMaster running and do not uninstall the existing version either. Just run the downloaded installer over the top. This should refresh the RailMaster files including the DLL ones and refresh the Windows Registry entries.
This screen shot shows the correct Download link to use
TIP: As a newbie poster on the forum, just be aware that the 'Blue Button with the White Arrow' is not a 'Reply to this post' button. If you want to reply to any of the posts, scroll down and write your reply in the reply text box at the bottom of the page and click the Green 'Reply' button.
See also – further TIPs on how to get the best user experience from this forum.