Hey lordi -
Welcome to IPB

Hopefully I can help as I'm doing a moving a large forum over from SMF as well.
Could not fetch remote picture fileThere are 2 possibilities for this type of error:
- In SMF there is a setting that allows users to them to use external avatars (in other words leave their avatar on the member's server.) If IPB cannot access this file, this error is thrown and the user's avatar will not be converted.
- There is also "Could not locate file" error, which is the same as above except it is a local file (the user uploaded it to your server and IPB cannot find it.)
Neither of these are critical per say, but can be annoying for your members if they have to re-upload their files. If you have a lot of these errors you might want to check the path you told IPB to look in for avatars. A typo in this could mean that none of your members have avatars
Report was referring to something deletedThis is likely due to a post / topic that was deleted, but the "Report to a moderator" report was never deleted. In this case, you shouldn't have to worry about it.
##: Starter not found.This is saying your members were deleted, but their private messages were still in the database. This isn't a big deal either unless you are getting this for all of your PMs.
Category / Forums "error"If I remember correctly I had the same problem, but I didn't look into it at the time. I'm currently importing around 250k users, but once that is done I'll be importing the category & forums and will take a look. You can also look under
/cache/converter_error_log_[date].cgi for errors.
Photo thumbnails errorThis could be for a number of reasons, the first I would say is to check to see if you have PHP-GD installed (the graphics processing library for PHP.) If you login to the admin section, then go to Support -> Diagnostics -> Overview and check to see if you have "gd" under the "Loaded Extensions"
One other tip - I turned on the DEV mode whenever I'm working on a conversion. This will allow you to see any specific errors when converting (e.g. a bad database query, missing files, etc.)
If you're still stuck, you can always open up a support ticket with the support guys in the Client Area.