Since it works locally, it is probably not a scripting problem, but rather a server problem.
The first thing i would check is the the Images/Artists/ folder that the files are being uploaded to exists on the server, and that it has read write permissions for all users.
if the Images/Artists/ folder does not exist on the server, you should create it.
Then in the files panel set the view dropdown to remote view.
Right click the Images/Artists/ folder and select set permissions. make sure that all three users have read and write permissions on that folder.
If upload is still not working, we'll have to troubleshoot further.
First, on the insert page, change line 56:
$WA_redirectURL = "artists_Detail.php";
$WA_redirectURL = "";
Next add the following at line 1:
finally, on the bindings tab, expand the Uploaded Files Global status group and add the debug info binding to the page.
post back any php errors that are occurring and the debug info aafter trying a test.