Have a .bat file which needs to run as Administrator, but the option under properties is greyed out. Why is that when I have local admin rights on the computer?
I think there are different techniques involved when running stuff as admin. For applications, there is the compatibility tab. Those settings are stored in the registry. You will probably see some applications listed on your machine:
A batch or cmd file is not an application. It's a script run by the application cmd.exe. Thus it is not handled by the application compatibility settings in the registry.
Further the batch-file has no way to store the information, that it should be run as admin.
But there's another way to do it:
Note that even in the shortcut properties, the run as administrator is grayed out on the compatibility tab. The runas-option is stored in the shortcut (.lnk) file.
On a side note
You could actually set the grayed out run as admin checkbox in the registry:
Create a REG_SZ key with the full path to your batch file and "RUNASADMIN" as value. (... or probably easier: check the 256 color option in the properties and edit the registry entry.) But this won't work. At least not for most files. That's probably why it was grayed out on the compatibility tab in the first place.
Anyway that's just what I deduced for me. I found no official documentation on this.