The error Message is most likely this (translated):
MeltyBlood is not installed.
MeltyBlood must be installed to play.
If you did not install the original Melty Blood correctly, you will get this error. What method did you use to install Melty Blood? Also, if the English Melty Blood patch is installed, you will get this error. Remove the English patch and replace it with the original Nero0623, or the original MB.exe file.