Hello,
You should try to identify what changed in your configuration that led the images not to be received anymore.
Have you upgraded one component of your network devices, has your system administrator changed a network parameter, has some firewall been added, have you upgraded the version of some software/hardware,...?
The "Receiving Association failed: DUL network read timeout" indicates a problem with your network infrastructure. Try to run Orthanc on the same computer as RadiAnt, and to turn off all of your firewalls for testing. Also, carefully follow the troubleshooting guides:
In either case, you'll most probably have to hire a professional who could test and debug your infrastructure:
Finally, consider getting in touch with the support team of RadiAnt:
Sébastien-