how can i fix the following error?
Try to uninstall it, and click install again. (click the red cross from your screenshot).
If that doesn't work, can you please try to uninstall Keil and install it again? I just installed the device pack that you refer to without any issues. My Keil version is 5.26.2.0:
At least that was the case in an old case that I found:
The solution was to install a later version of Keil. If you are already on the latest, perhaps you can try the same version that I use?
Alternatively, you can try to download the device family pack separately. You can find them here:
https://www.nordicsemi.com/Software-and-tools/Development-Tools/nRF-MDK/Download