Date range formula showing with VALUE or 0 result

[Aisling]

I am consistently getting a VALUE error or 0 back for the formula below

=SUMIFS(I2:I9999,G2:G9999,">"&A395,G2:G9999,"<w"&B395)

Column I is value (cells format = number)
Column G is Date (cell format is long date range e.g. 2013-01-01)
Cell A395 is start date (cell format is long date range e.g. 2013-01-01)
Cell B395 is end date (cell format is long date range e.g. 2013-01-31)

I have copied and paste the values into a new sheet re-formatted the above columns and still not working.
Any help greatly appreciated.