This VI has subroutine priority selected in the Execution page of the VI Properties dialog box. It cannot use an asynchronous node on its block diagram. Asynchronous nodes, such as dialog boxes, are supposed to allow other VIs on the same thread to continue to execute while they wait to complete their own execution. However, subroutine priority VIs block the execution of other VIs on the same thread until the subroutine priority VIs finish execution.
To correct this error, change the execution priority of this VI or remove the asynchronous node. To change the priority, right-click the VI icon in the upper-right corner of the front panel or block diagram window and select VI Properties from the shortcut menu to display the VI Properties dialog box. Select Execution from the top pull-down menu of the VI Properties dialog box and change the priority in the Priority pull-down menu.