Cannot train on MIRFlickr dataset

Hello! I have tried to replicate the training on the MIRFlickr dataset, but I have received the following error: 
ValueError: Dimension 3 in both shapes must be equal, but are 3 and 4. Shapes are [?,256,256,3] and [?,?,?,4]. Which is triggered in line 75 in network.py. Do you have any hints to how to overcome this problem?
