A good friend and colleague discovered this issue. An iPhone configured to sync with a Microsoft Exchange server would not permit any edits to calendar items. All other Exchange data could be edited without problems.
A recently released and very large firmware update was installed in an attempt to resolve the issue, however this did not help.
Oddly enough, the problem was caused by capitalizing the name of the server in the dialog box that configures the iPhone's connection to the server. Once the server name was corrected, all was OK.