For clarification, I can access the first 250 layouts, however, anything after that is inaccessible up to the final layout. I found this link which appears to describe a similar situation. Has anyone conquered this problem?
This is a known limitation of FileMaker on Windows systems and is documented in the Known Bugs list. When in layout mode, you can get to Layouts past the 255 limit by dragging the "bookmark" or clicking the book icon to change layouts just like you would change records in browse mode. In browse mode, you'd need to use a script to access the additional layouts, or you could limit the number of layouts listed in this drop down when in browse mode to less than 255 as you normally do not need to access that many layouts when in browse mode.
For More Information see: http://filemaker.custhelp.com/cgi-bin/filemaker.cfg/php/enduser/std_adp.php?p_faqid=548
This is one of many acknowledged bugs that can be found in the Known Bug List here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html