Suppose you have created a tab object for your form and discovered later that it disappeared after you compiled your database. It's possible that you assigned the title of the tab object from the Choice List without declaring the tab variable with a compiler command.
When you assign a Choice List to a tab object, 4D will assign the reference number of the list to the tab-object variable. When you run your database in interpreted mode, 4D has an ability to create the variable and/or change its type to match the value that is being assigned to it. In a compiled database, all variables must be declared in advance and given a specific type. In this case the reference number to the list must be declared as a long integer type.
To declare a tab-object variable, simply place the following declaration in your form or project method before the form is displayed. If you are using 4D Compiler with the "Process and interprocess are typed" or "All variables are typed" compilation path, then place it in one of your COMPILER methods.
See: 4D Compiler Reference