It's my web server. And it does have permission.

If you are getting a No Permission error then your server disagrees with you.

Is there a way to make it so it only keeps the last 5 backups so it doesnt fill the server?

Yes, or at least to keep only the last 7 backups. Someone else gave me this solution a while back in this thread.

AdminCP >> Settings >> Options >> vBulletin Automatic Backup

Combine Files
Set to yes to combine all tables into one backup file. = Yes

Date Format
Backup file date format (See http://uk.php.net/date). = N

Files Prefix
Backup files prefix, this is applied to all files. = FORUMNAME

GZip Files
Attempt to GZip the backup files after they have been saved. This may or may not work depending on your server environment. = Yes

What this does is create a series of backups with the format

FORUMNAME-digit-Full-Backup.sql.gz

where digit is the number of the day of the week, i.e., 1 through 7.

Once that change is made to options, as the backups are created they are saved with that format. If the filename doesn't exist, it is created. If the filename already exists, it is overwritten by the new backup. Thus, you always have the latest 7 days of backups and no more.

This works perfectly. I've been using it for several months now.

I posted the some thing a long while back, but I think I suggested using "l" (lowercase L) which is the full name of the day of the week (i.e. Sunday, Monday etc).

That would probably be more clear... if I'd known you could do that. :o

As an aside, I currently use the week number (W).

This means that I always have a current daily backup, and it "automatically" leaves me with a weekly backup as the number changes at the start of each week.

But that would mean you would have 52 backups at any one time, wouldn't it?

I just use the date of the month, so I will always have at least 30 backups consecutive. I dont need anything older and if I feel I do, I should be backing up at least once a month all backup files. But I dont.

Well if you kept them all on the server, yes.

I dont, I download them once a month and then delete older ones.