Hello jrball,
For any given CustomDisplayControlStyle the size of the .bmp specified by the Image_TransparencyMaskFilename attribute needs to be identical to that of every one of the specified Image_StageNN_ImageFilename attributes. I.e. all specifed stages' .bmp files need to have the same size as the specified mask.
If you're certain that's definitely the case (e.g. because you copied the whole CustomDisplayControlStyle object exactly from the CODM ODF of 'example custom organ 2'), then note that you can also get that error if you change a CODM ODF but its OrganID isn't unique and/or when loading it (via 'Design tools | Load custom organ') you didn't tell Hauptwerk that the organ's cache needed to be regenerated.
Image files are stored (along with audio samples) in organ caches, to allow faster loading. However, if you change anything in your ODF that relates to images or samples, then you need to make sure that when you use 'Design tools | Load custom organ' you have both of the following options ticked, so that Hauptwerk knows that the cache is no longer valid (because of the changes made in the ODF) and so needs to be regenerated:
- Force source samples to be loaded, bypassing the sample set cache
- Force source images to be loaded, bypassing the sample set cache
(If those options aren't ticked then Hauptwerk will by default read the images from the existing sample set cache, which may result in images being loaded that are no longer the intended ones for your changed ODF.)
(There's an old topic on the subject here: viewtopic.php?f=13&t=5190 .)