I'm a noob too so others might know more than me, but I would use the command prompt to rename the "UR" or "FMPUR" file in your runtime solution folder to a .fmp12 ext... example: database.ur or database.fmpur rename it to database.fmp12
I have fmpa 13 so the runtime has a .fmpur file but from what i've read it used to be a .ur file...
then it should allow you to find it in the developer binding prompt.
You can select the file extension that the runtime uses on the database, and as stated by Todd Nolan, 12 and 13 uses fmpur by default. This is the same database with a different file extension. Change the file extension back to fmp12 so filemaker will recognize the file as a filemaker database.
A runtime to run on Windows must be created in Windows, and a Runtime For Mac must be created on a Mac.
The Date File component of a Runtime, whether the runtime was created on Mac or Windows can be opened on either platform. It is not necessary to change the extension to open it. FileMaker Pro or FileMaker Pro Advanced will be able to open.
I create on my Mac. Then under Windows I make runtimes. But I will periodically open the runtime data file back on the Mac to update the structure, layouts, or scripts. Then I send it back to the runtime folder on Windows. NEVER an issue.
This has worked on all versions .. from 10 to 13.
As I stated above the database doesn't change (except the file extension) so yes it can be open on either platform just like any database created with filemaker. If the file extension is not the standard file extension for the database then when you click browse to see the file you will not see the file listed, so you have to change it back or type in the full name with the file extension. You can design on either platform you desire. I see no reason to over complicate things. A Windows runtime will not run on a Mac nor will a Mac runtime run on Windows.
S Chamblee is right. Its simple. The .UR or .FMPUR (by default) will open up in filemaker pro/advanced and you can edit/add/remove data from it. BUT, it will not populate in the developer utilities menu when your adding the file you'd like to create a runtime by. This is the point where you'd need to rename that file extension to .fmp12 for example. It's simple. Once you've done that, you can rebind the database file as a mac or windows edition.