Unfortunately I have also found Web Start shortcuts to be fragile for various reasons. It helps to classify the issues and their likely causes and solutions.
Unable to launch the application
Symptoms:
You attempt to launch a web start application by clicking it's shortcut, Java starts and then you get an error like the following Windows example:
Application Error
Unable to launch the application. [!]
Details / Exception: CouldNotLoadArgumentException
Details / Wrapped Exception: java.io.FileNotFound Exception
You go to the cache location and the file is not there.
Problem:
Someone or something deleted the cached jnlp file that the shortcut was pointing javaws at. "Helpful" cache clean up programs like CCleaner, Java updates that change cache locations, or user modifications to the Java control panel "Temporary Internet Files" will do this.
Fix:
Just re-install by revisiting the JNLP URL. Java 7 created web start shortcuts are more robust due to their -J-Djnlp.application.href option to the shortcut target.
javaws has been changed or moved
Symptoms:
On Windows you would get a message like the following one from Windows 8:
Problem with Shortcut
The item 'javaws.exe' that this shortcut refers to has been
changed or moved, so this shortcut will no longer work properly.
Do you want to delete this shortcut?
Problem:
Something deleted javaws.exe from the previously good location. Most likely a Java update on an x64 version of Windows where they seem to randomly choose between System32, SysWOW64, and Program Files as good locations or on Mac as you transition from Java 6 by Apple to Java 7 by Oracle.
https://forums.oracle.com/forums/thread.jspa?threadID=2526581
Fix:
"Uninstall" and "Reinstall", or (on Windows) delete all shortcuts (including any in your start menu) and then use the Java control panel Java Cache Viewer to re-create the shortcuts. If you don't delete all shorcuts created by JWS, it will not re-create the missing ones on re-install and the "Create Shortcut" button in the Java Cache Viewer will be disabled.
Fails to create shortcuts (Windows)
Symptoms:
Re-installing does not create shortcuts and the Install shortcuts button of the Java Cache Viewer is disabled after the user "deleted the (JWS) program".
Problem:
One of many shortcuts was deleted, one or more remains. Likely the program was "deleted" by simply deleting the desktop shortcut but a start menu one still exists.
Fix:
Delete the other shortcuts your jnlp file creates and then "reinstall" or use the Install shortcuts button of the Java Cache Viewer.
Fails to create shortcuts (Mac)
Symptoms:
Installing does not create shortcuts.
Problem:
Java Web Start launching seems broken during the transition from Apple's Java 1.6 to Oracle's 1.7. The systems that have both 1.6 and 1.7 are especially messy to troubleshoot, but even the pure 1.7 systems don't work.
https://forums.oracle.com/forums/thread.jspa?threadID=2516454
Work-around:
Download the jnlp file. You may need to use curl if you don't have a browser that is willing to save it as a file. Then double-click this file to launch.
There are other edge case errors like the Windows 8 shortcut icons that seems to now be fixed with 1.7.21_0, but those are the main ones that we see as "periodic errors when launching from Web Start" outside of self-inflicted personal firewall software trouble.