Looks like either some firewall/antivirus is blocking that address/port or some app/process is occupying it. If you google phrase "An attempt was made to access a socket in a way forbidden by its access permissions" you will see all kinds of reasons for this reported.
You can try to start r2la on different port. Start r2la by running rF2 Log Analyzer ver. 2.058.23\web2py\web2py.exe file. In the "Server Port" field try entering values different from 8000. Try some of these: 3000, 8080, 4200, 8100, 8200 (or theoretically any other number between 1024 to 49151).
You can try to find what process is using 127.0.0.1:8000 address. Start "cmd.exe" in windows (through start menu find/run field for example). In cmd window enter command netstat -o (also you can try netstat -ab). Look for 127.0.0.1:8000 address in the listed results.