Regarding the mp4 problem, I would suggest installing the latest K-Lite mega pac from here:
http://www.codecguide.com/download_k..._pack_mega.htm
I would uninstall the old version then re boot your computer before installing the latest one to get a complete clean install.
The other problem missing cdgs files.
Where they imported as KMA or KMH types ?
If they are kmh types open the folder in Windows explorer and check that each missing file has a kmh header file with a matching name.
Example: mp3+g should have an mp3 file a cdg file and a kmh file, three files with the same name apart from the extension.
A zip file should have just 2 files one of which has a .kmh extention.
If all the files are there try this even if they are kma types.
Open the rebuild dialog and look down the list of folders in the bottom left window and scroll to the file path of the missing songs. Select that file path so that it highlights then select Rescan folder.
Then when it finishes note whether the dialog that pops up states found xx songs or no songs found.
If the file path is missing from the list use the Add folder button to add it.
If it still doen’t list them open the folder again and look for the “ImportedFiles.txt” and rename it “BKUPImportedFiles.txt” . Then repeat the rescan function again.
You can also check the folder for any other .txt files error.txt files and read them in notepad. might give you a clue
See how you get on with that first.
If they list ok after that you can delete the “BKUPImportedFiles.txt”
This some times happens when you have duplicated disc ids or book ids.