I often run into an issue when updating SAPA when using a mapped network drive as the data store. The issue is the installer cannot see any free space on the network drive so shows an error asking you to clear more space, naturally you check the network drive and find there's plenty free.
The cause it due to the installer running as Admin, or another account and that account not having the network drive mapped. The solution is to run CMD as that user, or administrator and map the network drive using the command Net Use.
Here's a screen shot showing the command, just replace the server and network drive as required.