Repeat not working inside another tell block

I'm writing a script that will check that an external drive is mounted on boot, and then when it is to run drop box. I noticed when I first wrote the script with

tell application id "com.getdropbox.dropbox" to activate

It didn't always activate? So I found this to make sure it did

on is_running(appName)

tell application "System Events" to (name of processes) contains appName

end is_running

repeat

set safRunning to is_running("Dropbox")

if safRunning then

exit repeat

else

tell application id "com.getdropbox.dropbox" to activate

end if

end repeat

Then I put it inside a check for the volume drive. Then I get this? Any ideas please?

is_running("Dropbox")

--> error number -1708

Result:

error "Finder got an error: Can’t continue is_running." number -1708

on is_running(appName)

tell application "System Events" to (name of processes) contains appName

end is_running

tell application "Finder"

set allDisks to disks

repeat with theDisk in allDisks

if name of theDisk starts with "CloudStorage" then

repeat

set safRunning to is_running("Dropbox")

if safRunning then

exit repeat

else

tell application id "com.getdropbox.dropbox" to activate

end if

end repeat

end if

end repeat

endtell