These kinds of things always seem to be the last to be added to the documents. I saw in a recent blog post that someone had gotten a staging table error and they weren't sure what it was.

Here are the staging table error codes thanks to our great support engineer Pam Matthews

ERR210000           OK          
ERR210001          Error - duplicate code in source data.      
ERR210003          Error - code does not exist or has been deactivated for selected domain attribute.           
ERR210004          Error - code does not exist for selected domain attribute.             
ERR210006         Error - inactive member code.    
ERR210007           Warning - redundant assignment; transaction will not be logged.              
ERR210008           Error - may not stage inactive parents.   
ERR210009           Error - member code does not exist.       
ERR210010         Error - target code does not exist.            
ERR210011        Error - target code may not be leaf when staging parent relationships.   
ERR210012        OK - new relationship record.     
ERR210013         OK - new collection record.         
ERR210014           OK - relationship removed (moved to unused). 
ERR210015           Error - Children must be unique in Non Mandatory Hierarchy.     
ERR210016         Warning - unable to assign relationship or recursive relationship.              
ERR210017          Error - user name is invalid.         
ERR210018         Error - Model is required or invalid Model.           
ERR210019      Error - model administrator privileges are required to stage into the selected model.      
ERR210020     Error - Entity is required or  invalid entity name. 
ERR210021           Error - member type ID must be 1 (leaf member), 2 (parent member), 3 (collection), or 5 (collection member).           
ERR210022         Error - system attributes may not be updated via staging.             
ERR210023          Error - file attributes may not be updated via staging.     
ERR210024        Error - attribute value exceeds allowed length.  
ERR210025     Error - data is the incorrect datatype for requested attribute (must be Numeric).              
ERR210026         Error - data is the incorrect datatype for requested attribute (must be DateTime).            
ERR210027                 Error - data is the incorrect datatype for requested attribute (must be Integer).                
ERR210028        Error - invalid attribute name.    
ERR210029         Error - attribute value is required.            
ERR210030     Warning - attribute value will be unassigned.      
ERR210031         Error - Attribute_Value must be either ''Active'' or ''De-Activated'' when attempting to change the member status.  
ERR210032        Error - hierarchy is required or invalid hierarchy.                
ERR210033        Error - collections may only be staged to entities that have a hierarchy.  
ERR210034          Error - selected MemberCode is a reserved word. Please select another code.   
ERR210035           Error - code is required without a code generation business rule.              
ERR210036         Information - code is not required for a code generation business rule.  
ERR210037       Error - member type ID must be 1 (leaf member), 2 (parent member), or 3 (collection). 
ERR210038           Error - hierarchy is required if member type is 4; or invalid hierarchy.       
ERR210039        Error - member type ID must be 4 (hierarchy) or 5 (collection).   
ERR210040          Error - member code is required.              
ERR210041          Error - may not use reserved code ''ROOT''.         
ERR210042          Error - may not use reserved code ''MDMUNUSED''.       
ERR210043           Error - target type ID must be 1 (parent) or 2 (sibling).    
ERR210044      Error - target code is required.   
ERR210045         Error - may not use reserved code ''MDMUNUSED'' in non-mandatory hierarchies.          
ERR210046           Error - may not stage a sibling of the Root node.                
ERR210047           Error - may not stage a sibling of the Unused node.         
ERR210048           Error - member code and target code may not be the same.       
ERR210049       Error - may not stage siblings for collections.       
ERR210050      Information - hierarchy is not required for collections.    
ERR210052       Error - The member cannot be deactivated because it is referenced by an entity.              

I'm sure these will show up in the documentation at some point, but for now there here for your reference.