Hi all,
I have installed a boards package via the board manager. The first entries look good and work. Further down, there are a lot of identical entries that lead to an error when compiling.
The additional entries are not displayed in the arduino ide.

How can i remove these entries?

Many thanks Tim.
I have seen the issue with two board packets so far, the one was the radino, the other one was the mightycore pack.
radino: http://library.radino.cc/Arduino_1_8/package_radino_radino32_index.json
mightycore: https://mcudude.github.io/MightyCore/package_MCUdude_MightyCore_index.json
Please find the report for radino enclosed.

Seems there is a further error if i compile:

cc1.exe*: error: -fno-fat-lto-objects are supported only with linker plugin 

Within the Arduino IDE it is compiling without any issue.
Please let me know if you need further information and again a big thanks for looking into - i really love visual micro and the option of using Visual Studio for Arduinos.

While we investigate further, to work around the issue with the Radino Compilation:
1) Right Click on the project in Solution Explorer
2) Add > Add Local Board.txt
3) Add the below entry to the file and save it

} 

4) Try building again