Could be a mode switch problem, you could try Servisol video 40 on the switch, or it might need replacement.

There are a number of "checks' made during the loading process to insure that the tape is not damaged should the VCR have a problem. If any of the checks fail, the cassette will be ejected as you describe. Since there are many possibilities for this behavior, I can not state for sure how to resolve this problem. These units are usually quite reliable and are probably worth a repair estimate. Take this in and get a detailed repair estimate. Armed with that diagnosis, we should be able to walk you through the actual repair.

Dan