My guess is the issue of date is directly related.

What date format do you use? What is the standard for your locale, as opposed to your preference?

This is a try.... Change your date format to the USA, that is where Yahoo is based and we all know Citizens of the USA are not aware others do things differently....l that will be MM-DD-YYYY and then export your ICAL file and try importing to Yahoo.

Hey Matt,

Thanks for the response.

I've changed my settings in Control Panel to English (US) from English (UK). Restarted Thunderbird, and can see that the date formats have changed to US format of MM-DD-YYYY.

I then ran an export in .ICS format.

Cross checking the newly exported file with one taken with a UK locale, and the files are identical - in fact all the dates that I can see within the file are in ISO format YYYYMMDD.

So much for that bright idea....

I it is not to personal could you email me the ICS file so I can play with the lightning and yahoo stuff? I will have to get lightning working again. But that is over due anyway. (I use daily builds and all add-ons have regular issues)

Clicking on one of the pictures of my ugly mug will show my profile here with email address. (Don't be tempted to use the forum IM feature. It is not good for such things.)

Thanks for the offer of help Matt,

It seems to be one step forward two steps back....since everything seems to have imported successfully into Yahoo calendar, I thought I'd try deleting the instance of the calendar from Lightning, and then re-setting up the link to the Yahoo calendar.

Bad idea! Created a new calendar with the link to Yahoo, entered my password in the pop up box, and it's created the empty calendar in the left hand panel, but it's greyed out. I can change the properties to set the checkbox "Switch this calendar on", but as soon as I click OK, it momentarily activates, then deactivates itself....

Tried setting up a link on another instance of Lightning on another PC, same issue.

I'm completely flummoxed now!

Right - quick update - sorted out the issue with the calendars not connecting to Yahoo...stupid mistake on my part.

However this strategy didn't work, as the calendar has only sync'd one item - the most recent item I added to the diary yesterday.

No other items have been downloaded from the Yahoo calendar to the local instance.

This would seem to indicate that's it's a sync-ing issue to me?

A further update - as I've persevered.

After a frustrating few hours, I decided to scrap the whole thing and start again.

However rather than use an export from my local Lightning calendar as a source, I decided to export the Yahoo calendar (which has all the items in it), and use this as the source.

After the export, I deleted the Yahoo calendar, and started again.

I set up a link to the now empty Yahoo calendar. Then imported the Yahoo export file to populate the calendar via Lightning, with the expectation that this would replicate then into the Yahoo calendar.

So far so good.

Checked the Yahoo calendar - and everything has imported correctly.

Check back on Lightning and again, it's all OK. Check back a little while later - hey presto all the non-anniversary items in the local version of the calendar have disappeared prior to 16th May - ie 6 months to the day.

I'm going to try another experiment - importing the export into a new yahoo calendar and seeing what happens there.

But this seems to point to some sort of hard coded cut off period to avoid downloading the entire calendar.

Another update - exactly the same behaviour with importing directly into Yahoo and then replicating into Lightning.

Anniversary items are present, but nothing prior to 6 months ago has been sync'd.

Not sure if this is a Yahoo or Lightning "feature".