Each table prefix already exists.

[PesiV]

Hi. With advance sorry for my English.
I have a problem when installing CMS. When you configure the CMS database Table Prefix I have a message already exists. Come on changing it, the message appears.

[Sharley]

The table prefix is usually used when you have only one database available like on a Hosting service and you have to add tables from other different applications.

So in your case there is no real need to add table prefixes and if you do, then this naming convention usually overcomes any issues, like so:
prefix_tablename

I create a different database for each of my CMS, WordPress etc, and so there is no need to add a table prefix.

Good luck.

[PesiV]

Unfortunately, installing CMS asks you to fill the field with the name prefix

[Sharley]

Unfortunately, installing CMS asks you to fill the field with the name prefix

What does the CMS do if you leave it blank?

Just put an underscore like so
_
or use the first letters of the CMS like so
cms_
I use
wp_
for WordPress
pbb_
for phpBB forums.

Get the idea?

BTW which CMS are you referring to as this question should be asked of the tech support or on the CMS forum?

Best wishes.