Power BI Report Server Oct 2020 – “Same key already added” error on refresh

If you’ve upgraded to the October 2020 release of Power BI Server, you might be seeing the following error when you refresh some of your reports:

[0] -1056505856: COM error: mscorlib, An item with the same key has already been added..

This error appeared when we install the November 18th patch for Power BI Server (15.0.1104.264) and wasn’t present in the original October 2020 release. The especially frustrating part was that reports refreshed just fine in the Power BI Desktop client, and the issue only appeared after publishing the report up to Power BI Server, making it much more difficult to troubleshoot.

However, the resolution ended up being pretty straightforward – there are two different ways to define a connection to a SQL Server database, and if you use both methods in the same data model and then merge the results, Power BI Server has a problem with it (and Power BI Desktop does not). To correct this issue, you need to pick a method and ensure that all the SQL Server connections in your data model use this single method to connect to the database.

One method is used when you specify a database server, but don’t specify a database:

SQL Server connection with no database specified

This results in the following M query, with the connection taking up the first two lines (one for server, one for database):

M-query showing two-line database connection

If you specify the database in the connection window instead, it merges the connection statement onto a single line and uses Sql.Database (singular) instead of Sql.Databases (plural). Since you’re required to specify a database name when you provide a SQL query, so a custom query always uses this one-line method to connect:

Connection window showing database name
M-query database connection merged into a single line

Regardless of whether you enter the database name (and have the one-line connection method) or don’t enter a database (and use the two-line method), it looks exactly the same in the step window in Power Query:

“Source” is the database connection, whether it’s one or two lines. Navigation is the step that specifies the table/view you’re connecting to, and is the “MyTable” step in the examples above.

I’d recommend using method two for all your connections, as that’s what’s needed to run a specific SQL query – if any of your data sources and query-based and not just selecting a table, you’ll have to use this approach.

I hope this helps somebody else! While I’d love it if Power BI Server avoided errors like this one, I’d also really appreciate it if Power BI Server and Desktop used the same code for shared functionality so that you can be aware of issues before you publish your reports and they fail to refresh.

This took some frustration to resolve and I’m thankful for finally finding the resolution to this issue through a bug report that “JeanMartinL” had filed: https://community.powerbi.com/t5/Issues/BUG-Report-Server-refresh-fails-if-data-source-are-created/idi-p/1528954. Whoever you are, thank you!


Removing columns named “Column” when importing Excel files with Power Query

When importing Excel files using Power Query, any columns without a name in the first row will end up titled “Column123”, with an number at the end that increments for each column. This happens whether they contain actual data, or whether they’re just formatted columns that contain nothing at all.

Example of imported Excel file with two named columns and two just called “Column”.

If you’re importing a single file, you can rename or delete these columns as you need to. However, if you’re importing an entire folder of Excel files or the format changes unpredictably, you may want to automatically remove all o these columns at the end.

To do this, you’ll use the “Advanced Editor” to add a line of M-code:

"Remove Columns Named Column" = Table.RemoveColumns(#"Promoted Headers", List.FindText(Table.ColumnNames(#"Promoted Headers"), "Column")), 
After adding the new step, columns named “Column” are now gone.

After you add this step, you may need to modify your “Changed Type” step to only set the type on columns you’re keeping, as it automatically mentions every single column by name.

Adding this step will remove the additional columns, dynamically, every time the data is imported. Now when you import a folder full of Excel files and some of them contain additional columns or rogue formatting, the step will drop them if they don’t get named.

Powershell command to get current sessions on an IIS site

After a Powershell session at SQL Saturday (Phoenix #131) this weekend, I’m now suddenly on the lookout for handy powershell commands. The first one lets you see the number of Active* sessions on your IIS site (* because HTTP is stateless, it’s really the number of connections that have been opened recently – not what’s currently active, which is likely next to zero. I tried browsing around on a test site and it showed only my one user connected).

To get the currently active user count, here’s the powershell:

# Ensure you use the server's actual name, not LOCALHOST, which won't work
$Servername = "Your Server Name"
$Sitename = "Name of your IIS Site"

Get-Counter "\$ServerName\web service($SiteName)\current connections"

Get process ID for IIS App Pool

Ever try to debug something on a machine with many w3wp.exe worker processes and weren’t sure which one was yours? There’s a command line you can use to tell which is which:

In IIS 6 (Windows XP/2003), type:

iisapp

It is located in C:\Windows\System32, which is almost always part of the PATH variable, so you can run the command from anywhere (like iisreset).

In IIS 7/7.5 (Windows Vista/7/2008/2008R2):

appcmd list wp

It is in C:\Windows\System32\Inetsrv, which is not in the PATH variable by default, so you can switch to that folder first and run the command.

If you’re running multiple app pools on the server with the same proxy user account, now you can tell which one owns the application you’re trying to debug!