I can get in via computer with no problems.
When you try to log in on the phone does it say anything about a bad username or password? What does it do after you have pressed the login button?
Make sure you have logged out of Facebook on your PC.
Clear your phone browsers cache by doing the following...
1. Open "Internet" or whatever the browser is called on the Droid X.
2. Press the physical "Menu" key on your phone and go down to "More" and then "Settings".
3. Go down to "Clear cache" and press it. Say OK to the confirmation.
4. Return to the browsers main screen.
Try logging in again on the phone by going to the address I gave in the post above. If you still cannot get in it is likely one of two things. Either...
a) There is something up with your keyboard and it is sending the wrong characters.
b) Something or some setting is blocking the Facebook cookie.
You can also try with the official Facebook app by first making sure all it's data is deleted before you login. To do this go into Settings, then "Applications" and from there "Manage applications". Find Facebook in the list of installed apps and select it. There will be an option to "Clear data". Clear it and come out of the settings and then re-attempt to log in via the Facebook app.