lbshell can't handle xtrn sections with no available items (doors)
If the sysop has an external program section defined which the user has access to, but there are no external programs within that section (or none that the user has access to), then lbshell displays "No items with a return value!" and locks up.
The error appears to be coming from the alert() call on line 396 of load/lightbar.js.