It seams tht you aren't getting the correct permission on the files you are transfering to ISPConfig. Archive (with tar command) the Mambo installation from the old server and copy the archive to ISPConfig. Then you unarchive it from ISPC. That will preserve the file permissions and group/owner name so the script can be executed. If the file permissions and owner is not allowed in ISPC, you need to chown all the files and directories. Read the mambo docs for the correct chmod on specific files and folders to be changed in Mambo as well.
For the Mambo database, you need to go to the dev site and read the correct way to backup the mambo db. The backup in phpMyAdmin needs to be configured and exported a certain way to be able to import the db to the new server properly.