I had a similar problem when I changed my password on the remote repository.
Here is how I fixed it on Eclipse on Mac:
Important Note: These instructions have the side effect of clearing all passwords and other secure information. I was fine with that, but you will want to consider that before you follow these instructions.
Click Eclipse -> Preferences on menu. Expect a popup window called Preferences. Expand the "General" tree item. Double click the "Security" tree item. Expect the main pane of the popup to change to "See 'Secure Storage' for..." Click 'Secure Storage'. Expect the main pane to change to tabbed window. Click the "Contents" tab. Click "Delete". Accept a warning that all your secure information is deleted. Click "Cancel" or "Apply" to exit the popup window. Click the 'Git Pull' icon and expect to be prompted for username and password.