It's popular to play on multiple accounts simultaneously these days, but trying to do so, you may encounter the following errors:
1. "Unable to create advertising" (when launching multiple clients).
2. "Login limit exceeded: too many connections from your address" (when trying to log into the lobby or the same game world)
There are a few ways to get past this.
Method 1 (recommended)
Solution to error 1:
Change permissions on browsercontrol.dll to read only. Open your .jagex_cache_32 folder, typically found in:
C:\Users\%USERNAME%\.jagex_cache_32
Right click browsercontrol.dll, select properties and tick the read only attribute and apply the changes.
Solution to error 2:
Change permissions on random.dat to read only. Open your %USERPROFILE% directory (it's the same as C:\Users\%USERNAME%). Right click random.dat, select properties and tick the read only attribute and apply the changes.
Method 2
Solution to error 1:
Write a batch script (.bat) in e.g. notepad to fire up all clients simultaneously:
cd C:\Users\%USERNAME%\jagexcache\jagexlauncher\bin
set clients=5
:loop
Start "Runescape" C:\Users\%USERNAME%\jagexcache\jagexlauncher\bin\JagexLauncher.exe runescape
set /A clients=clients-1
if %clients%==0 goto exitloop
goto loop
:exitloop
exit
Change the number of clients (set clients=5) you'd like to fire up in the script. Save as type "All files" and add the .bat extension to the name, e.g. multilog.bat, then simply run the batch script you have created.