Problem reading ads1115 with non-default address

I'm using the DFR0553 ads1115 board with a RaspberryPi. Its i2c bus works with other devices. i2cdetect -y 1 shows that the ads1115 board is present at 0x49.

I'm using the non-default address of 0x49 because something else is at 0x48, the default address. I followed the instructions that came with the board, and there were no errors UNTIL I run ADS1115_ReadVoltage.py. At that point I get:

Traceback (most recent call last):
File "ADS1115_ReadVoltage.py", line 19, in <module>
adc0 = ads1115.readVoltage(0)
File "../DFRobot_ADS1115.py", line 142, in readVoltage
self.setSingle()
File "../DFRobot_ADS1115.py", line 110, in setSingle
bus.write_i2c_block_data(addr_G, ADS1115_REG_POINTER_CONFIG, CONFIG_REG)
IOError: [Errno 5] Input/output error

How do I fix this ?

Thank you in advance.