Expression Validator Not working correctly

I have a form upload control with the following RegularExpressionValidator.
<asp:FileUpload ID="upFile" runat="server" /> <asp:RegularExpressionValidator id="RegularExpressionValidator1" runat="server" ErrorMessage="Not an accepted file type (Currently only word, excel, and pdf documents)" ValidationExpression="[a-zA Z0_9].*\b(.doc|.DOC|.docx|.DOCX|.pdf|.xls|.xlsx)\b" ControlToValidate="upFile"></asp:RegularExpressionValidator> <asp:RequiredFieldValidator id="RequiredFieldValidator1" runat="server" ErrorMessage="This is a required field!" ControlToValidate="upFile"> </asp:RequiredFieldValidator>

When a user uploads files it has always worked, but recently, a file with this name triggered it to error, yet still allow the docuemnt to be uplo ...