Walmart's system returns many different kinds of errors and it can be hard to diagnose exactly what is wrong with your listing. More often than not, the issue stems from one or more of the fields in the "Category" tab of your listing.
Specifics will vary depending on the category you are listing within. The example below may not match your listing exactly, but should be similar to what is causing your listing to return this error.
If you are listing in Walmart's jewelry category, you will see a "Chain Length Measure" field and a "Chain Length Unit" field. Neither of these fields are required, but it's always good to provide as much information as possible.
However, if information is provided for one of these fields, the other becomes required. Because you are telling Walmart the length of your product is 16, they'll want to know if you mean inches, feet, etc. On the flip side, if you are telling Walmart that the unit of measure is inches, they'll want to know how many inches. This is why providing information for only one of these fields will return an error.
Similarly, if you have provided a value in the "Chain Length Measure" field that is "16 inches", this will also return an error. This field should only contain a number, while the "Chain Length Unit" field should contain the actual unit of measurement, such as inches or feet.
Walmart may also be returning this error if your description has exceeded the maximum number of allowed characters (4,000).