<p>I'm generating ICalendar (.ics) files.</p>

<p>Using the UID and SEQUENCE fields I can update existing events in Google Calendar and in Windows Calendar <strong><em>BUT NOT</em></strong> in MS Outlook 2007 - it just creates a second event</p>

<p>How do I get them to work for Outlook ?</p>

<p>Thanks</p>

<p>Tom</p>

I'm using Entourage, so this may not match up exactly with the behavior you're seeing, but I hope it helps.
Using the iCalendar from your reply, Entourage wouldn't even import the data. Using a known-good file, I got it to import, then successfully update. Comparing the two files, the only structural differences are as follows:
My known-good doesn't have a
```
VERSION
```
element
My known-good doesn't have a
```
PRODID
```
element
My known-good doesn't have a
```
STATUS
```
element
My known-good doesn't have a
```
SEQUENCE
```
element
Since Microsoft's support for open standards tends to lag, I'd suggest trying without the
```
VERSION
```
info.