Windows support software could not be saved to the selected drive
Cause

Apple allows Windows Installation, by first copying the entire ISO into a temporary storage area.  Most of the time it works, because there is enough space available.

When we use a larger ISO, like the 32-bit + 64-bit Windows ISO, it requires about 6.5 GB just for the storage, let alone uncompressed files usage.  Apple tried to download Windows support software onto that partition.  This is where the issue happens.  The package requires at least 1 GB, and it would not get it because of the ISO.

Solution


Use the 64-bit ISO (3.5GB) instead of the 32-bit + 64-bit Windows ISO for a x64 MacBook (all current generation ones) 
Use the 32-bit ISO (3.5GB) instead of the 32-bit + 64-bit Windows ISO for a x86 MacBook (2011 etc.)