I'm facing the issue with the above exception is gone through the below KB
https://community.appian.com/support/w/kb/294/kb-1069-legacy-designer-designer-does-not-load-properly
This didn't help me, not sure why I'm getting this error. This causing the runtime data page is not loading.
Its an on premise installation.
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hen I tried with the fresh Installation of 17.2, I got that issue Many Times,I Installed 16.3 version and then upgraded to 17.2 I don't see that issue now.