Unreal Engine 4 is available for Win10 UWP app dev now

Since that HRESULT begins 8007 the low-order short is a traditional Win32 error code which you can find in winerror.h (or on MSDN, e.g. here). In this case, 0x70 is ERROR_DISK_FULL.

If you have another drive with more space you can change where new apps are installed in the Settings app (System->Storage->Change where new content is saved).