I noticed when converting pages that I would sometimes get the following cryptic message (and this halted the import):
The PHP functions fopen() and file_get_contents() have both failed. We can't import any files without these functions. Please ask your server administrator if they are enabled.
FYI: This message appears when the program hits a file of 0 bytes... perhaps you could check for a file greater then 0 bytes before importing, and if the file is 0 bytes provide a message at the bottom informing the user of the file.