Since each newly released voicebank will use the latest copy of the software engine they are intended for, occasionally installation problems will occur between older and newer versions of the Vocaloid engine. Luka is one of the most common Vocaloids prone to causing this error and it often can be seen in both legal and illegal copies of her software. This appears relatively often with Luka because, as she possesses both an English and Japanese voice synthesis engine, so she will have problems with both English or Japanese vocaloids installed after her that were made before her.
When installing Vocaloids, it is usually advisable to pay a little attention to their release dates, just in case minor installation problems occur like this. The solution to this problem is simply to uninstall and re-install all Vocaloids in their correct release date order.