Q: iTunes keeps crashing on my iMac using OS 10.11.4 forcing me to force quit. Does anyone else have this problem and how can I fix it?

iTunes: Troubleshooting issues with third-party iTunes plug-ins - https://support.apple.com/HT203395 - hold down the Option and Command keys (on Mac OS X)

Hold down the option/alt key and create a new, test library. If iTunes starts your old library file is corrupt and will need to be replaced from a backup or rebuilt from scratch.

Linc Davis Feb. 2016 - https://discussions.apple.com/message/29767369#29767369

Reinstall iTunes:

- Apr. 2015 Niel post: Re-install iTunes application - https://discussions.apple.com/message/28055467#28055467 - delete the old application first, with instructions on how to do that. 

- April 2015 LincDavis post with a bit more detail on the method Niel outlines - https://discussions.apple.com/message/28101611#28101611

Do a backup, using either Time Machine or a cloning program, to ensure files/data can be recovered. Two backups are better than one.

Try setting up another admin user account to see if the same problem continues. If Back-to-My Mac is selected in System Preferences, the Guest account will not work. The intent is to see if it is specific to one account or a system wide problem. This account can be deleted later.

Isolating an issue by using another user account

If the problem is still there, try booting into the Safe Mode using your normal account.  Disconnect all peripherals except those needed for the test. Shut down the computer and then power it back up after waiting 10 seconds. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. When you reboot normally, the initial reboot may be slower than normal. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart by using the application un-installer. For each disable/delete, you will need to restart if you don't do them all at once.

Safe Mode - About El Capitan

Safe Mode Startup – El Capitan.

Holding down the Option and Command keys on opening iTunes worked immediately : no crash !

After quitting I launched it the usual way and everything was OK.