When creating custom fields, some field names are already in use by MetaLocator, in that they have special meaning.  This article summarizes those special field names.  These field names should also not be used after removing the underscore, for example, user_id implies that user_id and userid should not be used in your custom fields.

id
keyword
limit
radius
limitstart
tags
tag
component
task
location_id
layout
tmpl
view
cmd
framed
value
option
title
sourcefile
description
type
published
reviewanytext1,reviewanytext2 and so forth
tag1, tag2, tag3 and so forth
category1,category2 and so forth
group_id
groupname
taggroupname
tag_id
sku
user_id
itemid
isdirty
ignore
geofailed
tld
name
publishstart
publishend
datecreated
mlwpostid
slug
locale
region
retailerid
retailersid
username
password
location_type
timezone
mltable
groups
user_group_id
​