I2C not working with 2 devices

Projects Networking, Protocols, and Devices
1

I have these

Alone they work well, but when I plug them together the Arduino can't detect neither the Wave Shield or the RFID Shield.

Used a "I2C address scanner". Got this:

When I have Arduino + RFID
I2C scanner. Scanning ...
Found address: 36 (0x24)
Done.
Found 1 device(s).

Arduino + Wave Shield
I2C scanner. Scanning ...
Found address: 68 (0x44)
Done.
Found 1 device(s).

MOST IMPORTANT: Arduino with RFID Shield and Wave shield at the top
I2C scanner. Scanning ...
Found address: 36 (0x24)

Finds an address, but not a device.

Any tips? I need to fix this ASAP, for a school project.

I just want to play a sound when certain RFID Tag gets detected, nothing too complicated.

Thanks.

2

Do you have pullup resistors on SDA and SCL?

Pete

3

el_supremo:
Do you have pullup resistors on SDA and SCL?

Pete

I don't know what that is tbh.
It's my first time working with arduino. I just stacked the modules.

Read this in the Wave Shield data sheet:

SDA Input HIGH if the audio is playing
SDA is ：
Arduino UNO: AD4
Arduino Leonardo: D2

Does this means that it uses the port just for playing ad4 files?
In that case I can disconnect it, and use .wav instead?