Error: Internal Server Error apex

While saving a request in the apex ui using form button getting internal server error

I have configured a page with interactive grid where i have configured a col to as display only and added a target link to another page (my another page is configured as modal) and save button with type as page Submit.

Here if i configure my other page as modal , then on click of save i am getting Internal server error and unable to save
below screenshot : other target page modal (Page 32)

if i configure my other page (target page) as normal page, then error is not coming and i am unable to save . Please suggest