I am using Teensy 3.6 connected to a custom radio receiver unit. I have a transmitter unit which is transmitting data. The program works fine when I am using the serial monitor. However, everything locks down when I am writing data to an SD card. The command SD.open is returning false every time I am using it. The SD card writing function works fine if I use it separately with another program. I am writing a string and have tested it int but nothing works. I am using the SD.h library. Is it a timing issue or a hardware issue? Please let me what you think. thanks!