I'm using Samsung GT-i5503 with android version 2.2. I recently updated my Kies application. And after updating when I tried converting videos using Kies Video COnverter from youtube then saved in my phone, it won't play and error message was displayed(Sorry, this video cannot be played.). However, before updating my kies it works perfectly. How can I convert videos now so that can be played in my phone.
I highly recommend Handbrake Video Converter. It can convert all common video formats to mp4,mkv that the samsung video player supports. Choose the iPod Profile which is supported by most phones or you could also create your own profile. I always use Handbrake to convert videos for my Galaxy Ace. The Samsung GT-I5503 shares many similarities with the Galaxy Ace and as Samsung is using the same Layer of Software on top of android (TouchWiz with all the Apps such as Music,Video etc..) the same settings should work for your phone.
MX Video Player supports quite a number of video extensions namely .3gp .avi .divx .f4v .flv .mkv .mp4 .mpeg .mov .vob .wmv .webm .xvid and many more but it will require you to install this codecs for GT-I5503 (you will be auto prompted after you install the player but in case not, use the link).
You will not need to convert videos anymore.