Not able to save a Sales Invoice - Naming Series Requiered

I’m completely new to ERPnext and digging in to the install for the last few weeks. I hope to be able to change our current ERP system with this platform.

While learning how ERPnext works and doing occasional adaptations to accomodate our internal workflows I think I’ve broken something. Please bear with me as I’m a newbee…

Anyway, the problem I have is that I can’t save a Sales Invoice. When I want to save I get this error:

currently the Naming > Auto Name field in the Sales Invoice DocType states:


As you can see in the image above, the Series is there filled in, but it is not working. I’ve been looking on the forum for the last hours to find a solution, but beside a complete re-install I don’t know how to tackle this.

Any help is appreciated!

It appears that I encounter the same issue when adding a new Asset.

when saving I get the Message

Could not find Asset Name Display: (Name of newly added Asset)

It was me messing around in the naming and adding a naming field to pull information from another DocType. The link did not work and broke the functionality.