cats

Hi Cats!
Running version 5.1.2 of Blesta and Cerb 10.0.5 I was able to reproduce part of your problems. I went ahead and opened an issue on GitHub: https://github.com/SolidNetSoftware/plugin-cerberus/issues/5 and fixed what I could reproduce:
Enforce services to be selected by users This should remove the "undefined index" error you were getting. 
I was not able to reproduce any of the other errors you mentioned. I created a client that has 2 services and one that 0 services. The client with 2 services is able to select the services from the drop down without issue and switch between them. The client with 0 services will see an empty dropdown and the Create Ticket button is disabled.
If you have a custom theme, I am guessing that is what is causing issues. Hopefully the new version I released will offer more compatibility with custom themes.
Please let me know either way.
https://github.com/SolidNetSoftware/plugin-cerberus/releases/tag/v1.3.1
Follow the upgrade process here: https://docs.solidnet.software/blesta-cerb/getting-started/upgrade/
 
-Adam

FYI: Blesta-Cerb plugin 1.3.0 released and it supports Blesta 5.0.x
 
https://github.com/SolidNetSoftware/plugin-cerberus/releases/tag/v1.3.0
Follow the upgrade process here: https://docs.solidnet.software/blesta-cerb/getting-started/upgrade/
 
Cerb 10.x testing is starting now.
-Adam

Thanks Adam. Really appreciate your quick response and fix, especially as it's a plugin you've provided for free.

Cats,
Plugin has been updated to address this issue. v.1.20 has been tested and releasted with the latest version of Cerb and Blesta 4 series. Blesta 5 support is being test now.
https://github.com/SolidNetSoftware/plugin-cerberus/issues/1
https://github.com/SolidNetSoftware/plugin-cerberus/releases/tag/v1.2.0
Follow the upgrade process here: https://docs.solidnet.software/blesta-cerb/getting-started/upgrade/
Thanks,
-Adam