This will fix the errror / warning: lightmap need to be recomputed, it will be rejected in a future update
Open a Command Prompt from the directory that ManiaPlanet is installed.
The following command will now convert all of the Canyon maps that are in the C:Users/YourName/Documents/Maniaplanet/Maps folder, so make a backup first! and only place in there the maps that you want to convert.
ManiaPlanet.exe /computeallshadows /upgrademaps /useronly /fullcheck /LmQuality=Ultra /titles=TMCanyon
When ManiaPlanet launches, choose silent and your maps will start to convert, this process is not quick!