When you create a business rule (BR) you'll get the red cross to delete the rule:
When you enter more rules this works fine:
But when you enter a relatively long name, the red cross "disappears" (for all the rules):
When you select the grid to replace the rule with the long name you'll see the red cross is behind the other window:
For me, it was not possible to adjust the window size to show the red cross (tested on google chrome and IE11).
Workaround if you don't want to delete the complete BR:
Inspect the element, choose the "businessRulesLeftPanel" window, add 'width with 500px' and you can select the red cross:
(Adam Arrowsmith: It's not really a question, but more something I found and wanted to share untill this gets fixed.)