This kind of error typically is due to bad wiring of the sensor. The ADXLs are very sensitive (you might be tempted to say “overly bitchy”) when it comes to this.
Use a shielded ethernet cable (Cat 5E or above) and make sure you do a highly meticulous job when crimping or soldering the contacts.
A proven way of assigning the wires is:
- GND on Shield on the mainboard (MCU) side
- One pair for GND+MISO (SDO)
- One pair for 3.3V+MOSI (SDA)
- One pair for SCLK (SCL)+CS