Thank you for your post.
Since you mention Admin Console, FileMaker Server is being used. Is this also FileMaker Server 9? Is this running on Mac or Windows?
We have seen memory spiking to 100% when custom menus are implemented. Is the file being accessed using custom menus? Are there any plugins enabled?
Any other information you can provide may be helpful in narrowing down the possible cause(s).
Does it say that an object was autoreleased without an autorelease pool in place? What exactly is the line in the console log?