Dear all, I can't quite get safecopy to work with acid-state: old version of code : data T = T Foo $(deriveSafeCopy 0 'base ''T) new version : data T_orig = T_orig Foo $(deriveSafeCopy 0 'base ''T_orig) data T = T Foo Bar $(deriveSafeCopy 0 'extension ''T) instance Migrate T where type MigrateFrom T = T_Orig ... but when my (new) application reads the state from disk (written by the old application) I get "Could not parse saved checkpoint due to the following error: Failed reading: Duplicate version tags: [0,0]" When I change the version number in deriveSafeCopy, I get "Failed reading: safecopy: Map: Cannot find getter associated with this version number: Version {unVersion = 2}" I don't even know where the "2" comes from. Any hints appreciated - J.W.