You'll see that message in two scenarios:

1- The barcode you're trying to add has been incorrectly added to another SKU - here it needs to be removed from the other SKU so it can be added to the correct SKU

2- The barcode you're trying to add has been added to another SKU which is an alias of the SKU you are trying to add it to now - here the solution is to combine the two product records, so both SKUs are listed in one product. This is the only way a single barcode can be associated with more than one SKU.

The easiest way to see which scenario you are facing is to open the Products section and scan the barcode in question. (typing it in works too btw) The search result will be the item currently associated with the barcode.

Click the name of the item in the search result to open and edit it.

If the barcode should not be associated with this item just click the X beside the barcode to remove it. You'll now be able to add it to the other SKU.

If the item is a valid alias that should also be associated with the barcode you can use the alias feature to combine the product records.

What if it's a separate item, not an alias, and it has the same barcode? Ouch. In that case better see this article.

Is this happening a lot?

If you're having to go through this process with the majority of your products it usually means that many of your products have multiple SKUs and you can save time by importing them using a CSV file that associates the additional SKUs with the SKUs you already have in GroovePacker.