The problem with backups is that they are intended to be restored by the same version that created them. On the same machine architecture and OS too. You cannot use them to directly move from one version to another or between platforms. (Although some flexibility is sometimes found it isn't supported and won't help you in this case.)
It sounds like it must not be too big of a database. So have them send you a zipped copy of the database. All of the database. Make sure that they truncate the bi file first. On their box:
proutil dbname -C truncate bi
Then:
prostrct list dbname
This will create dbname.st -- in that file is a list of every file that needs to be in the zip archive. Make sure that your client gets them all.
Unzip it (life will be easier if you use the same path names) and then run:
proutil dbname -C conv1011
You will now have a version 11 database ready to take a look at.