54fce98f_ining___multidimensionalmayhem__Cause_Solution
[Error] 8. Multiple Key Sequence Columns – Deployment on a mining structure that uses the Sequence Clustering algorithm fails with the following error text: “Error (Data mining): Multiple sequence key columns were detected in the sequence table in the MyClusteringModel model. The Microsoft Sequence Clustering algorithm only accepts tables with one sequence key column.” [Cause/Solution] 
I may be making some kind of inadvertent error due to inexperience, but I have received this error repeatedly in various projects even when only one column has been designated as a Key Sequence. For example, in one particular project I have a DateID set to Key and a DateID in a nested table set to Key Sequence. It always generates this particular error unless I set the nested DateID to Key as well, which may unfortunately throw off the results of the algorithm. This is the only solution I know of to this strange error, which is at a minimum badly worded, if not an outright bug. Either SSAS is falsely detecting a second Key Sequence column, or it is detecting a different problem and returning an inaccurate message.
An Informal Compendium of SSAS Errors, Part 2: Data Mining | multidimensionalmayhem
Cause/Solution