Hello There,
Thank you for providing the access. I have investigated your site and to my eagerness to resolve this issue, I have accidentally deleted the plugin which have deleted your grid. I am so sorry about it. We can still revert it if we ask assistance from your hosting provider to revert the changes using the site back up in there.
I also discovered that there must have been something in your grids that resulted the issue. Because I have created a test grid and inserted it in a test page. In my test, there is no error and I have tried and tried my best to replicate the error and nothing. My test grid displays with no issues at all. I must say that your grid may have been created using the old version and there was something in it that resulted to the error. I cannot say which have caused it.
You can see the test page here: http://baumschule-vonderstrass.de/dev/baum/
Again, I am truly sorry for accidentally deleting the grid. I hope you could forgive me about my honest mistake.