This happens if the ISO is missing the SLPM_656.00 boot file. It means the download was corrupt. Redownloading from a different source is the only fix.
If you are specifically searching for the tag, you likely have one of three motivations: Download Iris no Atelier - Eternal Mana -Japan-...
The English localization (simply titled Atelier Iris: Eternal Mana ) is widely available on the secondary market for PS2. It is far easier to find, and the gameplay is 99% identical. This happens if the ISO is missing the SLPM_656