Error Characters (--) When Filtering
When you use slicers or context filters with a calculated
fact or measure, you may see two dashes (--) as values for some
or all of the cells in the report that represent aggregates that
are calculated in the database (aggregation is set to Automatic).
This means that the data source is unable to compute these values.
You can avoid this error by using an explicit rollup rule or aggregation function such as Total. However, do this only if you are familiar with the data and absolutely certain that this is the appropriate answer for that report.
Time Hierarchies
Error characters also appear in summaries if your report includes a time hierarchy and you use two or more members from a different time hierarchy as a context filter. To avoid the error, use only one member as the context filter.
Filters in Queries and Sub-queries
For dimensional data sources, filters in queries and sub-queries are considered equivalent. The same applies to slicers.