I have the exact same problem.  Unfortunately, no answer.

can anyone help?

Without actually seeing your data and various other things - hard to
pinpoint the cause. However, having said that, generally when we've seen
that kind of problem - it's usually been a data-related issue causing the
failure. Not knowing your versions either etc - could also be related to how
your version of the import/export wizard is translating the field types
since in some scenarios it will determine a field type to be something other
then what you're expecting it to be.

In short, (on the assumption that there are no system related issues with
your filters being corrupt etc), it can be a real hit-or-miss kind of thing.
You can try saving your Excel file as a CSV and see if that works better for
you. If it doesn't, then you may want to download one of our programs
(ContactGenie Importer or DataPorter) and import the file (the eval imports
the first 50 records). If there are any field name or data issues - these
will be reported in the CG log files which may give you a better clue as to
what the cause may be.

Karl