Help why can't I move files to the SD card?

[NewChinaHand]

My phone's internal storage is almost used up. My SD card, however, still has lots of room on it. So I would like to move several of the applications that are currently stored on the phone's internal storage to the SD card.
However, when I go to Settings > Applications > Manage Applications and then select an application which is currently stored on the phone's internal storage, it doesn't let me move it to the SD Card.
There is a button precisely for this purpose "Move to SD Card".
However, the button is greyed out. I am unable to click it.
Why is this?
How can I move these applications to the SD card?
By the way, I have a Samsung Galaxy Ace GT-S5830 running Android 2.2.1
Please see the screenshot of the Application Manager page with the greyed out button here

 

[Marcus_SwJ]

I have the flashlight apps too n it wont let me move to the SD card also... The same goes for the other apps. Did u installed alot of apps? Cuz I dun think it will eat up most of the space of the internal storage... However some apps or games are able to move to SD card...

 

[chanchan05]

Some apps CANT be moved to the SD card.