Hi Jonathan,
Thanks for your interest in Syncfusion products.
I am afraid that I am not able to reproduce the issue of the fatal error in the grid with the splitter. Also, I have created a sample to test this issue and please refer the sample in the link below:
http://websamples.syncfusion.com/samples/Grid.Web/6.2.0.40/Tools_ASP_splitterwithgrid/main.htm
Please try running the sample and if still the issue exists could you please try reproducing it in the above sample so that we could analyse further and sort out the cause to provide you a better solution?
Thanks,
Janagan.