Mask doesn't preview properly

[FONT=Times New Roman][SIZE=3]Hi, I’m relatively new to Flash, and I’m in the process of creating a flash intro to my website. The problem is, whenever I preview one of my Mask layers by pressing Ctrl+Enter, the mask effect doesn’t work – it merely shows the masking object.[/SIZE][/FONT]

[FONT=Times New Roman][SIZE=3]The puzzling thing for me, which leads me to suggest that the mask should work is that in the normal timeline view, when I lock both the mask and masked layers and press Enter or slide through the frames – the effect works perfectly. On Ctrl+Enter all of my other Masks work fine as well - the one in question has text as the mask content.[/SIZE][/FONT]

[FONT=Times New Roman][SIZE=3]It only stops working when I view it as an .swf file or play the movie with Ctrl+Enter. Does anyone know why this is happening, how I can get around it, or whether it will be a problem when published?[/SIZE][/FONT]

[FONT=Times New Roman][SIZE=3]Thanks in advance for any help, and sorry if it is a “noobish” question. :)[/SIZE][/FONT]