Kit-lens came with Canon Digital Rebel (original first model)

The lens itself won't corrupt your data. A bad lens would be unable to focus or be unable to communicate with the camera about focal lengths, aperture etc.
It is more likely the camera itself is starting to fail. The consumer Canons are only designed for around 100,000 photos - how many has yours taken? The 300D is quite old now, so will be starting to show its age.
How may CF cards do you have? If you a few, try them in turn, formatting each on the camera and seeing if you still get the errors. If you have another lens, try that also just to put your mind at rest. If all cards fail, the CF card interface of the camera could be failing. If you only have one CF card, get another (or two!!) and if it works OK, throw the old one away.
One extra piece of info: I had a 300D but upgraded to a 350D as the 300D has a nobbled CF interface making it about 6x slower. No point buying UltraII or UltraIII cards for the 300D as it just can't use them as intended. You really notice the speed increase moving to a 350D, but have to get used to the much smaller body size.