You cannot create old Guitar Pro projects (for example .gtp files from version 4) in the latest versions of the program, simply because it is not backwards compatible. So there really is no way how you could transform .gpx projects to .gtp files.
This conversion entry was verified by us and conversion was flagged as wrong or not possible.
Usually this happens when the conversion would try to convert different types of data between each other, such as audio to image, or it is not possible because incompatibility between programs, caused by closed file formats, very limited support etc.
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