having trouble with n5.5 freezing after about 3 hours, also i have to re-install the 5.5 update everytime i boot up in order for n5.5 to see video files.
Something is really wrong, this is a slave PC that runs Cubase 6 for 10 hour sessions without any issues.
just got a blue screen as well so lost the initial error message. 
hi indiescore,
not sure if this helps, but i was able to open a couple of 5.5.5 projects with v5.5.2 and 5.5.3. I didnāt get any error messages on opening. On saving it did mention the version discrepancy and hit me with a prompt about saving a ānew versionā, or āoverwritingā.
note: they were pretty simple projects - not sure if thereās possibly some new functionality in 5.5.5 that I hadnāt employed which might give you an issue if opening in an older versionā¦? (i.e. - attempting to open a 5.5.5 in 5.1 gave an error about some corrupt data).
also: iām on a mac so not sure if a pc would react differentlyā¦?
meant to add: i donāt have 5.4 so couldnāt try that specifically.
good luck!
hereās the error i received trying to open Nu 5.5 with Nu 5.1. (attached screenshot)
project opened, but warning about āproject could not be restored completelyā is pretty disconcerting.
not sure if 5.4 would give you the same issue - i would imagine soā¦?
Thanks for the input, I reinstalled FireWire drivers and that seems to have stopped the crashing, but still having issues with video not found due to invalid format with every boot up, every day, 