According to the description of the new GRC 0.70 release:
File Format - Saved flow graphs from previous releases lack the
necessary information to be used with the new block definitions.
Therefore, older saved flow graphs are incompatible with this release.
To alleviate problems, an xml validator will automatically reject older
saved flow graphs.
Although I think the new capabilities are a great idea, I find this
incompatibility to be very unsatisfactory. At this point, I have a
large library of Gnu Radio designs using GRC, and don’t want to have to
re-enter them by hand all over again. You shouldn’t abandon your users
like that. There should either be a converter program to upgrade the xml
files with info from the new templates, or an “import” option in GRC for
ingesting old xml files.
I think GRC is a great product. It acts as a “force multiplier”,
allowing a great deal more productivity in an R&D environment than
having to code changes in Python each time you want to try something