Updating dimensions when focus is lost from any of 9 columns
I don't do C# so pardon the syntax, but you should be able to reduce the amount of code by using a for loop over a string array with your column names. 

Again I don't do C# but in Java you could do something like this:

for(String col : new String[]{"article", "account", "dim_1", ...}) {
    if (e.SourceCol == _detailSpread.GetColNumber(col)){
        UpdateDimensionData(_detailSpread.GetColID(e.SourceCol), 
                            _detailSpread.Rows[e.SourceRow]);
        break;
    }
}


I would consider extracting the string array to a constant. 

Or if your table is static you could just use a HashSet (or whatever it's called in C#):

// Somewhere in a constructor or static initializer
HashSet&lt;Integer&gt; focusChangeColNumbers = new ...;
colNumbers.put(_detailSpread.GetColNumber("article");
colNumbers.put(_detailSpread.GetColNumber("account");
...


// Then do:

private void _detailSpread_OnCellFocusChange(object sender, CellFocusChangeEventArgs e)
{
    if(focusChangeColNumbers.contains(e.SourceCol)){
        UpdateDimensionData(_detailSpread.GetColID(e.SourceCol), 
                            _detailSpread.Rows[e.SourceRow]);
    _detailSpread.Validate();
}


Note that this is going to be \$O(1)\$ in the number of columns where the other options are \$O(n)\$ in the number of columns.

Another option (if the API permits, I have no idea) is to simply turn it around:

String[] focusColNumbers = new String[]{"article", "account", "dim_1", ...};
if(focusColNumbers.contains(_detailSpread.GetColName(e.SourceCol))){
    ...
}