[Plugin: WordPress Form Manager] Can't filter extensions for file upload

Hi,

I made a custom form with a file upload input. I would like to limit to some extensions (image like png, jpg, bmp…).
Whenever I try, it won’t let me put filters: it always says that i must put commas in my filter list.
I tried: “png, jpg, bmp” or “.png, .jpg, .bmp”, with or without spaces, I can’t validate my form.
I don’t understand where is the problem.
It let it a few days with no limitations and this morning of course i’ve been defaced. This time I can’t let it pass.

Thanks a lot for your help or explanations if I made something wrong.

http://wordpress.org/extend/plugins/wordpress-form-manager/