Can you just
save your magritte package in a new version to try
please ?
I can load the latest code from here (including Magritte-Seaside-lr.
153), so it should be ok.
Maybe you have a corrupted download in your cache? Try deleting the
files in the folder 'package-cache' and evaluate
'MCFileBasedRepository flushAllCaches'. If this doesn't help I will
commit a new version tonight.