A few hints for posting on this sub-forum:
1. This forum is for both users and developers. Please specify which you are, as it can help in formulating an appropriate response.
2. Always state the ModelGUI version you were using when the issue was encountered. This especially important because the code is constantly being updated (read: improved), and the solution may already have been committed to a newer issue. It is also very useful for developers to identify and track bugs.
3. Exceptions, errors, and warnings are text printed to the console, which give information about program execution and problems encountered therein. In brief:
a. An exception is a Java stack trace, which is distinguished by being a long list of lines which trace back program execution through the Java classes that are being executed. Stack traces are useful mostly for developers, but it is also very useful for users to post these here. It will look something like this:
Exception in thread "main" java.lang.NullPointerException:
at SomeClass.thirdMethod(SomeClass.java:15)
at SomeClass.secondMethod(SomeClass.java:11)
at SomeClass.firstMethod(SomeClass.java:7)b. Errors and warnings are produced by the ModelGUI to indicate a problem, without burdening the console with long stack traces.
4. There are different levels of logging which determine what gets printed to the console or to a log file (see this description). If something is going wrong but you are not getting an error or exception, you may need to change the init file (typically "init/mgui.{os}.init") to reflect a more verbose level of logging, and ensure it is being sent to the console. The most verbose option is:
# set logging
setLogFileAndConsole mgui_session
setLoggingType debug..which will write to both the console and a log file (located in the "logs" subdirectory), and will write everything, including all stack traces.
5. You can use the terminal window used to run your ModelGUI session to retrieve log output, or you can add a Console Window to one of your tabs in the program itself. Errors and exceptions will show up in red in this window, and can be copied using Ctrl-C.
6. Try to use the "code" buttons in the edit window to ensure your exceptions, code, etc. is encapsulated in a code block. This makes your post much more readable. Additionally, Wikidot provides a rich selection of formatting tools; feel free to use these to make your post easier to read, and respond to.