Sp_BlitzCache 678 not writing to table
If you pop open sp_BlitzCache, you should see parameters for:

@OutputDatabaseName NVARCHAR(256) = NULL ,
@OutputSchemaName NVARCHAR(256) = NULL ,
@OutputTableName NVARCHAR(256) = NULL ,


You seem to have tacked the schema name onto the table name. That's probably what's causing the problem.