Error: Save Failed: Field Input Error (Check Red Fields).

[BKesslerHHC]

I've just finished setting up a brand-new installation of Cacti 0.8.8f on Ubuntu 15.10. Everything is working as expected, except I cannot save any changes to my data source.

To reproduce the problem, I go to Console -> Data Sources, then pick one of my data sources. In the attached screenshot, it's a Cisco router that's working and graphic just fine; I've selected interface Gi0/0.6. I tried changing the name field to "Primary ISP" (without the quotes) and clicked SAVE. This results in the "Error: Save Failed: Field Input Error (Check Red Fields)." in the screen shot.

The same happens if I open any data source, make no changes to any field, and click save.

Anybody have any idea on what to do about this, or how I would report it as a bug?