[Koha] MARC check - item fields error

I have just installed Koha 2.2.7. However after defining the MARC structure and doing a MARC check, I got the following error. OK itemnum : the field itemnumber is mapped to a field in tab -1 item fields ALL items fields MUST : be mapped to the same tag, and they must all be in the 10 (items) tab OK Only 1 MARC tag mapped to items OK biblioitems.itemtype defined OK itemtypes defined OK homebranch defined OK holdingbranch defined OK biblionumber and biblioitemnumber mapped correctly OK no NULL value in frameworkcode TOTAL You have 1 error(s) in your MARC configuration. Please fix them before using Koha Has somebody come across the same error and how can it be resolved. Mary