Well, checksum errors on one partition after writing to another one or total loss of all partitions after writing to the disk clearly points to the 4GB problem.
PFS2ds might help here but PFS2 is not as stable as PFS3.
You should create an OS3.5 emergency disk, boot from it and reinstall the whole HDD with the new HDtoolBox. Make sure it uses the new FastFileSystem version 44. After that the data beyond the 4GB limit should be accessible and checksum errors should be gone.
If you fear the trouble you may also calculate where the 4GB border of your HDD is and leave the upper part of it free (without partitions). For 0.3GB out of 4.3GB this might be worth it.
However, there is the archive Check4GB on Aminet which will help you to check if everything is set up correctly.
Bye,
Thomas
