I have this annoying issue and I googled it but most of the solution only worked on 2003/2007. We are using 2010...
We have a public facing FTP server: ftp://schedule.test.com/ and our remote agents frequently login to the FTP with same common account to check the schedule, which is presented as excel file on ftp server. Every single time when agent click the excel file in IE and click Open when prompted, excel will present warning message. Here below is an example of the message:
Microsoft Office Excel cannot access the file 'ftp://schedule.test.com/06-June 2013.xlsx'. There are several possible reasons:
The file name or path does not exist.
The file is being used by another program.
The workbook you are trying to save has the same name as a currently open workbook.
The funny thing is, I click Ok for the message and the spreadsheet opens...
I am pretty sure the account used to login has read permission the the excel file on ftp server...
Please help and let me know if any other information you need.