without more details ....
could be you are running out of memory if there is any image conversion (thumbnails, resizing ,etc).
possibly increase php memory limits or disable any image conversio… (View Post)
There are several smart things you can do when you have an odd problem to try to isolate problem. You can use this technique all the time.
to determine if plugin , cache or theme is causing probl… (View Post)
If nothing else works, for an experiment. try downloading vanilla 2.1 and try to import into vanilla 2.1 and see if you get errors. then upgrade to 2.5 if you can successfully import.
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