error evaluating 'MaskDialog' callback of asynchronous machine block

error evaluating 'MaskDialog' callback of asynchronous machine block

Warning: Could not evaluate MaskDisplay commands of block 'untitled/Asynchronous Machine pu Units': Undefined variable "X"

or class "X.p1"

what can i do for removing this error? i am just inserting the block and trying to change the parameters . Using Matlab 2018a version.