I want to get results for one Store in EBAY-DE and also all results for the same Store in EBAY-UK. But there i got "Invalid store name."

What is wrong with the Request? Here are the two Links (API Keys removed):

EBAY-DE: http://svcs.ebay.com/services/search/FindingService/v1?OPERATION-NAME=findItemsIneBayStores&SECURITY-APPNAME=xxxxx&RESPONSE-DATA-FORMAT=XML&REST-PAYLOAD&storeName=BilligerLuxus+Shop&outputSelector=SellerInfo&GLOBAL-ID=EBAY-DE

EBAY-UK: http://svcs.ebay.com/services/search/FindingService/v1?OPERATION-NAME=findItemsIneBayStores&SECURITY-APPNAME=xxxxx&RESPONSE-DATA-FORMAT=XML&REST-PAYLOAD&storeName=BilligerLuxus+Shop&outputSelector=SellerInfo&GLOBAL-ID=EBAY-GB

Other Stores have not this problem and i got the Request (API Keys removed):

EBAY-DE: http://svcs.ebay.com/services/search/FindingService/v1?OPERATION-NAME=findItemsIneBayStores&SECURITY-APPNAME=xxxxx&RESPONSE-DATA-FORMAT=XML&REST-PAYLOAD&storeName=RBT+Shop&outputSelector=SellerInfo&GLOBAL-ID=EBAY-DE

EBAY-UK: http://svcs.ebay.com/services/search/FindingService/v1?OPERATION-NAME=findItemsIneBayStores&SECURITY-APPNAME=xxxxx&RESPONSE-DATA-FORMAT=XML&REST-PAYLOAD&storeName=RBT+Shop&outputSelector=SellerInfo&GLOBAL-ID=EBAY-GB

Is this perhaps a problem with the relevant Store/Account or with the API?