Hello Sanjay,
The error simply means the block sizes specified for the restore and the one used for the backup differ
from each other. The restore cannot be done.
Check the medium definition (block size) of the source system where the backup is taken from and adjust the block size for the medium definition of target system where you are doing the restore.
If you still having problem - please update the thread with the output of DBM command "medium_getall" from both source and target databases.
Regards,
Yashwanth