Rougy,
Some thoughts...
1) First you need to save the file to a folder on the server to which all users have access.
2) To guard against more than one user wanting to access the file at the same time, as well as guard against users saving (unwanted) changes to the file, you should use the "Properties" function to "write-protect" the file. This will allow users to open the file, but will force them to save the file in a directory of their own choice IF they want to save any changes.
3) IF, on the other hand, you want all users to be able to enter data into this file, and implicity SAVE the changes to the same file, then this suggests that your problem lies with some of the users NOT having access to the folder in which you placed the file.
Hope this "general" commentary helps. Hopefully, with this commentary, you'll be able to use it to either resolve your problem, or to provide FURTHER clarification regarding the SPECIFIC error messages you are getting.
Regards, ...Dale Watson dwatson@bsi.gov.mb.ca