This has really been a perplexing problem for some users. 
Two tips to get you started and then a series of steps to try and get your pedal and project working properly
- avoid using iCloud for your computer Documents and Desktop folders
- avoid connecting your pedal via the USB cable method; use your built-in slot reader or an external USB media reader.
Series of steps: (please try these steps in order).
- download and unzip a fresh copy of the Default Content Backup 2.1 to your desktop. BeatBuddy Default Content (SD backup).
- Insert your unlocked SD card in your computer slot reader or external USB media reader.
- select all content in your SD card and Move to Trash; Empty Trash. NOTE: do not use Disk Utility to ERASE your SD card.
- verify using CMD-Info that your SD card format is FAT32; if not, use Disk Utility to ERASE and set format to MS-DOS (FAT32).
- use the BBMO 1.5.5 (beta) to open the project folder you just downloaded and unzipped to your desktop: BeatBuddy Default Content 2.1 - Project BeatBuddy Manager Online BETA 1.5.5
- Use the BBMO (I use Vivaldi) to Sync to SD Card; when done, eject the SD card
- with power off on your BeatBuddy (BB) pedal, insert the SD card in your pedal
- power your pedal on
Still getting an INVALID SD CARD error message? Please reply with your results. If it still does not work, you’ll ultimately have to contact Support, support@singularsound.com for help.
If you do get it working, recommend not putting the Premium Library Content on a 4Gb SD card, rather, try using a larger, SDHC 32Gb class 10 card.
I am testing a possible fix by making an image of a working (on my Mac) 4Gb SD card with the BeatBuddy Default Content 2.1 - Project and should have it available this weekend. Depending on your progress, I’ll make it available for download with instructions on how to get the image on your 4Gb SD card.