Have you recently changed/formatted your SD card?
If no instrument definition file is present I would predict Pyramid to behave like this. The Pyramid needs at least one instrument definition file to exist in the root on the SD card in order for the ‘call instrument’ feature to work. Instrument definitions may be in separate files, or they may be in one file, as long as no more than 16 instruments are defined at any one time.
If you have added instruments to the definition file you should also check the syntax of the file. A simple error in the file may confuse the Pyramid, although the file parser seems pretty robust.
I suggest you take out the SD card and use a computer to check that the instrument definition file is intact and readable. The SD card may have become corrupt for some reason. Try putting your instrument definition file onto another SD card and see if that makes any difference. Always keep a backup handy - SD cards don’t last forever.
If the instrument definition file is intact and ‘call instrument’ still does not work, you should probably contact Squarp and explain the problem to them, as your unit may have become faulty.