To remove a guideline, make sure you click on the little triangle present in the rulers, and drag it outside the rulers. If you click the line itself, you won't be able to move it. It's possible that there may be multiple guidelines on top of each others, you may need to repeat this step a few times, depending on how many were added.
If you do this, you should be able to remove the guidelines. Let us know if you are still having troubles.
Raphaël Lalonde Lefebvre