"by the way: is there a way to check whether a variable is defined in Applescript???"

Change:

set eBayCal to (the first calendar whose title is "eBaytoiCal")
set createEbayCal to true
try
set xx to eBayCal
set createEbayCal to false
end try
-- by the way: is there a way to check whether a variable is defined in Applescript???
if (createEbayCal) then
make calendar at end of calendars with properties {writable:true, description:"eBaytoiCal", title:"eBaytoiCal"}
set eBayCal to last item of calendars
end if

to:

-- by the way: here is a way to check whether a variable is defined in Applescript!!!
try
set eBayCal to (the first calendar whose title is "eBaytoiCal")
set createEbayCal to false
on error
set createEbayCal to true
end try
if (createEbayCal) then
set theCalendar to make new calendar with properties {title:"eBaytoiCal", description:"eBaytoiCal"}
set eBayCal to last item of calendars
else
set eBayCal to last item of calendars
end if