Sorry people for no replies. I was busy lately and I didnt get a topic reply notification in my email soo... I'll take a look at each of your issues when I get some time. I'll deal with the easiest first. denskie war, you are getting this error because you made your table called phpbb1_backup but the script is look for a table names phpbb1backup due to your phpBB database extension. So just rename to table so it looks for the right one.
For the people that are looking for backing up their files, it is in the contrib directory. I do not encourage you to use the script on a account that has many files because the script might not support it.
For the people with high server loads, this script is very diverse. First off, it must execute a query to get the table names in your phpBB database, then it will execute another query for EACH one of the tables to get its structure which is the CREATE TABLE query. then a SELECT query is performed for each one of the tables too to make the INSERT INTO queries, which may take a lot of time if you have a large forum and for sure puts a lot of strain on the MySQL server. As you see it is pretty complicated.
If anybody has and ideas on how to make it put less strain on the server, im listening.
For now, I recomend you exclude uneeded tables such as the search tables which is usually more than half of your database. They can be regenerated using MODS that are out there. I would also exclude tables like logging tables, if you have a mod that does so because they also take up a lot of memory. I will be looking myself on how to reduse the server load.
If you the script isnt obeying the file limit you supplied, this is because the script is not running throught completely due to a PHP error. This may be because is exceeded the PHP error limit to keep the server load down. To prevent this from happening, I recomend you doing the same as above. I will look into that a bit more too.
Thanks, and sorry for the late reply