Framework Error: Cannot call method 'substring' of undefined

Hi

I'm using Architect3 to design my view. I put a chart into a container and get an ERROR like this:

design.jpg

It's from Design View, and when I switch to Code view, the ERROR is gone.

code.jpg

So is there anyone who knows the reason? It seems that the project is correct and can be built successfully. The main problem seems related to the Design view when a chart is involved.

Framework Error: Cannot call method 'substring' of undefined