Most recent build is 814!! Please update.
From the other posts to which you're referring, you will already have understood that it's caused by .dat files not being re-created after some change has been made to the main bitmaps (involving transparency).
In as far as I know both the rgn.dat and the rgnfs.dat files are generated automatically by BSPlayer.
Simply put all your bitmaps and ini-files for your skin in a folder e.g. MySkin which (similar as Base-skin) is a subfolder of "Skins"-folder.
Do not place any existing (previously created) .dat files in that folder.
Start BSPlayer and try your skin (incl. fullscreen-version).
Exit BSplayer. The correct dat files should be created by BSPlayer in your skin's folder now. If you change something in a main-skin lateron: simply delete the corresponding .dat file(s) and repeat as above.
If your skin is finished: zip the files (not the folder) and rename .zip extension to .bsz (making sure you haven't hidden the file-extension .zip to prevent that your renaming results in something like MySkin.bsz.zip).