We encountered a strange issue when connecting to analysis services through Excel where all of the row level sums were correct, however the total value was a negative, as per below:
As you can see the row level sums are all positives, but the grand total is a negative, why?
The underlying data is all positive, however the underlying datatype in the database is a small int, however there are 6 billion rows in the table.
The issue is that when SSAS sums those 6 billion rows of small int values the total ends up breaking the INT barrier (2,147,483,647) which Excel displays as a negative.
The measure group will inherit its data type from the underlying view and attempt to use that:
To fix this issue you need to alter the data type in the Source and then either leave the DataType in Advanced as Inherit, or change it to BigInt:
Now when you deploy and process your cube, the issue should be resolved!