[solved] Library Manager Error Message

I get the following error message:

package_index.json file signature verification failed
java.lang.RuntimeException: cc.arduino.contributions.SignatureVerificationFailedException: package_index.json file signature verification failed
 at cc.arduino.contributions.libraries.ui.LibraryManagerUI.lambda$onUpdatePressed$0(LibraryManagerUI.java:212)
 at java.lang.Thread.run(Thread.java:745)
Caused by: cc.arduino.contributions.SignatureVerificationFailedException: package_index.json file signature verification failed
 at cc.arduino.contributions.packages.ContributionsIndexer.parseIndex(ContributionsIndexer.java:94)
 at processing.app.BaseNoGui.initPackages(BaseNoGui.java:487)
 at processing.app.Base$8.onIndexesUpdated(Base.java:1328)
 at cc.arduino.contributions.libraries.ui.LibraryManagerUI.lambda$onUpdatePressed$0(LibraryManagerUI.java:210)
 ... 1 more
Index error: could not find referenced tool name=arm-none-eabi-gcc version=4.8.3-2014q1 packager=arduino
Index error: could not find referenced tool name=arm-none-eabi-gcc version=4.8.3-2014q1 packager=arduino
Index error: could not find referenced tool name=CMSIS version=4.5.0 packager=arduino
Index error: could not find referenced tool name=CMSIS version=4.5.0 packager=arduino
Index error: could not find referenced tool name=CMSIS version=4.5.0 packager=arduino

I completely de-installed Arduino, removed the Arduino folder in Documents, and installed Arduino 1.8.3,
but still get this error. What should I do?

The error message is not revealing the cause of the error.

Try this:

  1. Select File > Preferences from the Arduino IDE menus.
  2. Click the link following "More preferences can be edited directly in the file"
    This should open a folder named Arduino15 or similar.
  3. Delete all files in that folder other than preferences.txt.
    :warning: Please be very careful when deleting things on your computer. When in doubt back up!
  4. Restart the Arduino IDE.
  5. Select Tools > Board > Boards Manager from the Arduino IDE menus.
  6. Wait for updates to finish.
  7. Click the Close button.

Hopefully after that the error will no longer occur

Yes, this helps. Arduino startup, Boards Manager and Library Manager work flawlessly again. Thank you!