Problem fetching data from MPU6050
If you are using the MPU6050 library from jrowberg/i2cdevlib, the library does not have any kind of error handling, so it is unfortunately not easy to guess what went wrong, or even if something went wrong. If the getMotion6 function fails, it will simply copy corrupt data into your return values and it is not possible after the invocation to tell if the function succeeded and you got a valid reading, or if the function failed and you only got garbage back.

One possible problem is that the MPU6050 can be configured to use one of two I²C addresses (0x68 or 0x69) and you are using the default address, as implemented in the MPU6050 library (0x68). It might be worth to try the other address, in case your module is configured that way:

MPU6050 accelgyro(0x69);