thanks for your post - and sorry for the trouble that you are experiencing.
From your description, there are two things that could be causing this:
1.) You could be affected by the "Suhosin" problem, a PHP extension on your server that prohibits saving large tables. Please see the following threads for more, including ideas to fix it:
2.) You could be affected by a problem with the character encoding. Very likely this is a problem with the character encoding. I have noticed in the past, that certain characters (especially from foreign languages) seem to cause trouble with some PHP functions. This happens, when the plugin can't read the table data correctly from the database, which usually happens during the saving of the imported data. This might also be a possibility here...
I don't really think that other plugins influence this, as there have never been reports on something like that.