Application Forms Editor is not showing my Form but instead 291: Stacktrace:'

Application Forms Editor is not showing my Form but instead 291: Stacktrace:'

Please help,

After saving the form I just created, I wanted to make some more changes.. so I went back to the Forms tab then selected my form. Here I get to see the Basic Fields and Advanced Fields things on the left but my Form isn't showing up!! Instead I get the error text:  291: Stacktrace:'

Screenshot attached.