“The model is missing” ??

Hi,
I am a beginner with WordPress.
I installed WordPress both locally and on my remote site. On both locations, the blogs work OK with the default theme.
But I made my own theme, which works locally. Now I transferred all files in the same remote directory (wordpress/wp-content/themes/My_theme) but it does not work.
When I login as administrator, in the “appearance” tab, the available themes are listed, but mine is listed in another list : “Corrupted themes”. It says : “the model is missing”.
What does this mean ? What is “the model” and where is it specified ?
The problem is probably simple, but I could not solve it.

?? Gabier