Windows 7: Problems formatting portable drive

I have a 40 gb portable drive (Wolerine Brand) I use to transport files between work and home. I've been using it for 5 years now between my Mac computer at work and my Windows computer at home with no problems until recently. I figured the issues might have been from a corrupt file on the device so I decided to wipe it clean and reformat it. I did so on my PC with my Windows 7 operating system. I saved a folder of files to take to work which I could access with no problem, however, I could not copy anything to the drive. It said I had read access only. I brought the drive home and set the security permissions to full control. I tried the device again at work and again it says I don't have access to the drive. How can I format the portable drive so that I can use it with both computers?

First concern - five years for a drive is like a hundred dog years.

It is possible that the work machine has been set to disallow writing to external devices.

Techmom, when you reformatted the drive did you do it under OS-7
Also do you have OS-7 set to back up files on the portable drive?
I'm thinking out loud if the media id has changed and is un-recognizable at your work?

Yes I reformatted under OS 7. No I do not have the system set to back up to a portable drive. I've used this on both machines without an issue. Maybe the drive itself is dying?

Not quite sure what you are saying above, as OS7 is a Mac OS.

Nonetheless - can you attach any other known working storage device at the work PC and copy files TO it? If no, it is a system setting on the work PC preventing the action. If yes, be certain to format the external drive while attached to the work PC and test.

Your drive is old, and that is a concern, but the reported symptoms are not indicative of pending drive failure.

Yes I can attach other portable devices and read-write from them on both the mac and PC. The problems writing to the drive on the mac occurred after I formatted the drive on the PC with OS 7.