Invalid Item Number Warning while doing Item Import

 Hi,
I am trying to import Items and categories using Item Import Interface. I populate the mtl_system_items_interface and mtl_item_categories_interface table with the appropriate data. When I run the Item Import it ends with warning. Following is the error:

Message Name: INV_ICOI_INVALID_ITEM_NUMBER
Table Name: MTL_ITEM_CATEGORIES_INTERFACE
Column Name: ITEM_NUMBER
Error Message: Item number 51_A1003|1001 is invalid.

Now the item Number in both MSII and MICI table is identical, still I get this error.

Any pointers will be a great help.

Thanks,
Kumar