Within the area of effect, this spell impedes the use of spells of the summoning subschool and other effects that summon creatures. Any such spells, spell-like abilities, or similar summoning effects used within the area have a percent chance of failure equals 5% × your caster level, to a maximum 75% chance of failure. If the summoning effect already has a percent chance of failure (as is often the case with the summon spell-like ability of outsiders), these percentages stack. This spell does not affect summoners attempting to summon their eidolon, but it does affect summoners casting other summoning spells.