Please help me... on my admin area, while I select categories, this message appears on the top of the admin area: "Error: Catalog images directory is not writeable:....."

So, if I want to upload a new product images, I cannot upload the product images from admin area. I have to upload it from CP.

Firstly I think that CHMOD of the catalog images folder set to 644, but while I check it was set to 755, this makes a little difficult while I want to upload the product images, I have to upload it on File Managers on CP. Because the field for uploading images doesn't active.

I will be very thankful for those who can gime me some solution for my problem. Thank's...