Stringwidth is a PostScript operator used to manipulate text. This can be both text added in the lay-out application itself or text from an imported graphic. So some text element on your page is causing this error.
Try copying the entire content of the page to a new document.
Delete blocks of text or imported graphics containing text to determine what element caused the problem. Then recreate that block or graphic.
PostScript files created using this application can show limitcheck errors, offending command stringwidth. This only happens if images are included in the file. Apart from creating a file without images, there was no other known workaround when I added this description.