MSI does not support "Prepend to existing value" here
The installation action Prepend to existing value is not supported by MSI for some object types. To work around this limitation, InstallMate replaces this action by Append to existing value. However, this might not always be appropriate.
MSI only supports a subset of the generally available installation and removal actions offered by InstallMate. Moreover, the available MSI subset depends on the object type.
If Append to existing value is an acceptable substitute, you can ignore this message. Otherwise, select a different installation action for the object. Use the See also section below to check which MSI installation actions are available for each object type. Alternatively, build an InstallMate installer instead.