Applescript: Open current Safari tab in Chrome (Troubleshoot of working script)
Just because Safari and Chrome are running, doesn't mean that they have a window open. You can either test for open windows as Mark points out or simply issue the reopen command which opens a new window if one does not exist. 

tell application "Google Chrome"
    if not (exists window 1) then reopen
    -- insert your code 
end tell

tell application "Safari"
    if not (exists document 1) then reopen
    -- insert your code 
end tell


EDIT

tell application "Safari"
    if not (exists document 1) then return
    set theURL to URL of current tab of window 1
    close current tab of window 1
end tell

tell application "Google Chrome"
    if not (exists window 1) then reopen
    set URL of active tab of window 1 to theURL
end tell