This error can appear if:
You have exceeded the maximum number of columns allowed in a table or the maximum number of locks for a single file.
The indexed property of a field was changed from Yes (Duplicates OK) to Yes (No Duplicates) when duplicate data is already present in the table.
If the maximum number of locks per file was exceeded, you can increase the number by editing a registry entry for the local computer. However, this is not a recommended option.
Find the MaxLocksPerFile registry value using the Windows registry editor (regedit.exe) and increase the value. The MaxLocksPerFile value is stored as part of the following key:
HKEY_LOCAL_MACHINESOFTWAREMicrosoftOffice12.0Access Connectivity EngineEnginesACE
If you edit a value in the Windows registry, there is no guarantee that the change will not corrupt the registry and render Windows unusable. Edit the registry at your own risk. If you do, it is highly recommended that you make a backup of the registry before performing any edits.
If you have changed the Indexed property of a field and duplicate data already exists in the table, you can either reset the Indexed property back to the previous setting, or remove the duplicate records from the table.