This error can occur at any time, but generally it appears after listing the product to Walmart for the first time. This error can have a number of causes, but it may not appear in Listing Errors.
To diagnose the root cause of the problem, we can look at the Channel Status Explanation field for this SKU in QuickEdit.
First, go to Catalog > QuickEdit, then click "Add Column" and you can search for "Status" or "Walmart Status" and you will find the Walmart Channel Status Explanation field as well as Walmart Channel Status:
Here we can see the SYSTEM_PROBLEM Channel Status is indicating that Walmart has blocked the listing because of a "Trust & Safety" concern. In this case a value (very often the Title or Description) contains keywords that Walmart has rejected.
To resolve these kinds of errors, contact Walmart Support directly so they can provide you with the specifics on what needs to be corrected.
Additional information on listing products to Walmart can be found here.