[quote user="mapmap"]So I thought maybe I need to reindex the New Mail folder - I can't seem to be able to reindex the New Mail folder - no option to do this[/quote]

The new mail "folder" isn't a folder like the other ones, it's just a collection of new mail files, hence there's no index file which can be fixed in any way. And as your further attempts show that wouldn't have helped anyway as the problem appears to be inside the message(s).

[quote user="mapmap"]Then tried to open one of the mail items in this new Folder - 4.61 crashes[/quote]

If you can identify specific messages causing the crash (HTML formatted messages, BTW?) we would like to get them as unmodified as possible, preferably as zipped CNM files from your new mail directory (path shown on Help => About Pegasus Mail = Info as New mailbox location). As you may need to move or copy these messages (or a single one) back to the new mail folder please note that you can select a message via right mouse click to avoid being opened in preview mode for safely deleting it if you need to do this in PM 4.61. Right-clicking a message (in the new mail folder) and selecting Message properties will display the CNM filename of the message, BTW. Please send your report to beta-reports[at]pmail.gen.nz.

I installed 4.61 today over 4.52 , and it looked fine - like to new look-and-feel.

But I quickly noticed  that while trying to open a mail item in the New Mail folder (wasn't even a new download), 4.61 crashed. It poped up the usual screen with a "Debug" option. I clicked on it and nothing - So I guess I can't give any details.

So I thought maybe I need to reindex the New Mail folder - I can't seem to be able to reindex the New Mail folder - no option to do this, so I created a new Folder and moved everything to that new Folder - tried to reindex this folder and was sucessfull. Then tried to open one of the mail items in this new Folder - 4.61 crashes

 I reverted to 4.52 and everything is just fine, I can open any of the items in the New Mail folder, unlike 4.61.