train_* files not generated while training on my own data

I'm still practicing with this software and got stopped by some detail probably hiding somewhere in front of me.
When training on my own data, I found that the train_* files in the sample folder never get created. I see that those files are, indeed, created when training on the celebA dataset.
My dataset is made of 292 images, each of them RGB, 256x256px, png format.
I run the training with the following command line:
`python main.py --dataset=images --input_height=256 --input_width=256 --output_height=256 --output_width=256 --input_fname_pattern="*.png" --batch_size=11 --is_train --c_dim 3`

Where am I wrong? Any help is welcome, thank you very much.