The event type specified is either invalid or inconsistent with the operation or event properties specified. Valid values for event type can be either LINE or POINT. The event type might be valid, but it may be inconsistent with the operation. A good example of this can be seen when using the Overlay Route Events geoprocessing tool. If both the input and overlay event properties are type POINT, the output event properties must also be defined as POINT. Specifying output event type LINE in this instance would be invalid.
Ensure you have specified a valid and consistent event type for this operation. See Linear Referencing toolbox for links to the help for the specific linear referencing geoprocessing tool.