3605415 - I receive 'Error during update of linked process: Failed to upload to pex-backend' during Load phase of ETL/T&L

I receive the following error during Load phase of ETL/T&L in Process Intelligence:

"Error during update of linked process: Failed to upload to pex-backend. Reason: Target responded with 'Bad Request': The following process views reference attributes, which have been removed from the eventlog. Either add the attributes [x,y,z] back to the eventlog or fix the process views by saving them again [a, b_c]. This will remove the removed attributes from the process view." 

process, view, error, update, linked, process, upload, pex, backend, attribute, eventlog, transformation, t&l, etl, soe , KBA , BPI-SIG-PI-DM , Data model / ETL for SAP Signavio Process Intelligence , Known Error