Can't open my files in 5.4.1

I have Rapidweaver 5.4.1 and for some reason I cannot open my files at all. It says:

“RapidWeaver 5.4.1 uses an upgraded document format. If you save this document it will no longer be readable by earlier versions of RapidWeaver.”

I think i had 5.2.1 before as I have been using since 2011

and then: The document “my doc name” could not be opened.

I really need access to these - may ideas?