How do I check string for date in DAX/PowerPivot?

I have a column in analysis services which has manually entered dates in it. The users of the system aren't particularly good at entering information, and among the dates is a whole lot of rubbish, syntactically incorrect dates. I want to create another column of dates, that in PowerPoint I can convert to be a date column. To do this I need to do something along the lines of SQL's ISDATE check. Does anyone know how else I could get around it? I have tried =ISERROR(format(DATETOCONVERT,"Standard Date","01/01/2000")) which should replace dates it can't work out with an actual date, but this still won't let that calculated column be formatted as a date. Your help would be appreciated. Thanks