Commented Unassigned: Strange FileNotFoundException [9365]

I've got a worksheet with half a million rows. After writing values to cells in the first 20 rows. I call Save() on the workbook. That produces the following exception:

Could not find file 'C:\Users\nitew_000\AppData\Local\IsolatedStorage\dxiachod.3ue\sshwvvzf.hbs\Url.kxeclqde42apwq4041xfhhekihulkeam\Publisher.qolcwimjscmc2r1axln3vci10dth4a4y\Files\1vcczr3o.pnw'.

I just updated to version .74

Any ideas what file its looking for?
Comments: Download the source code and debug it so you can tell me which line throws the error. My guess is that it isn't ClosedXML but the FileStream class the one that's using error handling as part of the flow. When you turn on break on CLR exceptions the error is not caught by a try catch, instead it puts a break on the execution.