Try removing it from your server or web service/outlook first, and then reboot PC and battery pull phone--then try and delete it. See if that helps. Good Luck!
I was going to start a new question. But I know what Nasir is talking about. If you forward an e-mail on the 9900 Then you can not delete it later. If you resend service books or re-register on the internet and even a battery pull will clear (Delete) the messages but only until you send the next e-mail forward than the problem starts all over again. I noticed today when I forwarded a message. It saved the forwarded message with the original message as it should on the phone but also produced a duplicate copy of the forwarded message on the phone. And I can not delete any of the three messages off the phone. My e-mail is GMail and my phone provider is T-Mobile. What is also interesting is...That I just checked is... The original deleted forwarded message is showing in my GMail trash box as being deleted. But it is still on my phone, even though I told the phone to delete the message from both the phone and from GMail.
...Joel
"Menu>Display Style>Single Messages then delete the email." YEP!! I did this before I saw this message and yes it actually worked.
Actually I didn't need to delete the messages again...They went away as soon as I went to the single message mode.
I wish RIM would fix this bug.
Thanks.....Joel