I am unable to open Excel file (which is located on network share) from Finder using 'Open with...' -> Microsoft Excel (Windows X) when the same file has been opened by another user (e.g. on Windows PC).
I get an error message "File in use"
In order to solve this error you need to modify the file on the machine where it is already opened.
In Microsoft Excel (2010) go to File -> Options -> Trust Center -> Trust Center Settings... -> Privacy Options -> disable option 'Remove personal information from file properties on save' -> Click OK.
Open the Excel file (first instance). In Excel go to Review -> Share Workbook -> enable option 'Allow changes by more than one user at the same time. This also allows workbook merging.'
Open the file (second instance) from another location.