There are a number of ways to download data out of SAP and everyone has their own proven method for doing this. And usually the method that you prefer to use is the only method you were taught, thus you rely solely on that process.
But what do you do when that process stops working? Better question, why isn't it working that way anymore.
What I have found in my experience is that a user has inadvertently selected a default for the output and is unable to figure out how to reset the default. The steps to reset the default is simple, but only if you know the steps to get there. Otherwise, it can and will be frustrating to figure it out.
From the Open Line Items report for General Ledger accounts (FBL3N) the typical output of the report is rendered in a flat view.
The first step is to change the list view output. This is done via the menu under Settings -> Switch list
Now the output is shown in an ALV grid that has an excel look and feel. It is also easier to highlight and select data to copy from this view. You may prefer to have this output as your standard view going forward if it isn't already as it has some flexibility that the standard view does not provide.
The next step is to do a right click anywhere on the data selection to initiate the popup option box as shown below. Select the Spreadsheet… option.
At this point, you can either change the available format to the format you desire and/or uncheck the Always Use Selected Format checkbox to eliminate the selection default option going forward.
Here are the selectable options in the drop-down for formats.
If you select the Excel (in Office 2007 XLSX Format) option the report will open an Excel spreadsheet and populate the data.