Hello...
Some comments and things to check:
1. Barring some legitimate hardware problem, what you are trying to do should work just fine. I suspect some kind of interference between the drives and that the error is incorrect.
2. Be sure that one drive is jumpered as "master" and the other one is jumpered as "slave". The concept of master and slave is a standard. But, how the jumpers are done is not. Some master drives must be jumpered as "slave present" if a slave drive is present. Check your drive maker's documentation for information about this.
3. A new-style 80-wire IDE ribbon cable CAN designate "master" and "slave" if both drives are jumpered as "cable select". When "cable select" is used, the end connector on the IDE cable is always the master and the middle connector is always the slave.
4. If the above does not resolve your problem, try connecting only the new drive to the IDE ribbon cable (as master) and observe what happens. If it works, you still have a compatibility problem. If it doesn't work, it suggests the new drive has a problem.
5. The warning about the impending critical failure is likely coming from the SMART (Self-Monitoring, Analysis and Reporting Technology) diagnostics.
6. If the two drives are otherwise OK but cannot "make nice" on the same IDE ribbon cable, try connecting them to two different IDE controlles and separate IDE ribbon cables.
Does this help?
-----Steve Jackson
CEO/CSA
Software Corporation (Softcorp)
http://www.softcorp.us/probono
Advanced pro bono tools and utilities free for personal use