Can't get md5sum to work

[Ari Torhamo]

Hello,

Could anyone please help me to get md5sum work for me. I have downloaded
and burned Hoary array6 and would like to check if it's OK. When I do 

md5sum /dev/hdc

I get 

/dev/hdc: failed in buffer_read(fd): mdfile: Input/output error. 

This has actually always happend to me, already when I burned early
Warty CDs. The drive is hdc and it starts to do something and goes on
for a few minutes, but then I get the error message above. I have tried
different discs too, but it hasn't help either. There are no problems
using the drive othervise, it reads and burns without any problems.

Any ideas?

Ari