Error CNDL0199 : The Wix element has an incorrect namespace of 'http://schemas.microsoft.com/wix/2003/01/wi' - wix

Question

I migrated my WIX project from V2 to V4 and then changed the namespace in the .WXS files
I replaced the below namespace
<Wix xmlns="http://schemas.microsoft.com/wix/2003/01/wi">
with
<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
Once the changes have been made when i run the build installer i am getting the below error:
error CNDL0199 : The Wix element has an incorrect namespace of
'http://schemas.microsoft.com/wix/2003/01/wi'. Please make the Wix element
look like the following: <Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
E:\Code\EMR\Wix\src\EMR_Registry_entries.wx
I replaced the new namespace but it is not reflecting. Once i run the build installer it is setting with the old namespace. I tried multiple times but it is always setting the old namespace.
Please help me to resolve the issue.

Answer 1

UPDATE: Question that came up from a second read of your question.
Source Control: "Once I run the build installer it is setting with the old namespace." - are you sure the build process doesn't
auto-magically 1) check the WiX source out of your source control system? Or 2) maybe it is doing some XML manipulation via the automation script?
WiX Version: Are you sure you are compiling with WiX 4? Maybe you are compiling with WiX 2 or WiX 3 unintentionally? Try hard coding the full path to the WiX binary in your build system - if you have one. Please see this (Sean is a WiX developer): Migrate Wix Project to version 4.0. Frankly I am not sure how well WiX handles multiple-version installations on the same box combined with migrated sources (identically named binaries of different versions - WiX 2, 3, 4 - globally applicable via the PATH variable? Not sure).
Visual Studio / Cmd.exe?: Are you compiling with Visual Studio or via the command line? (I am not quite sure reading your question). Maybe try via the command line (towards bottom) if you are using Visual Studio - or vice versa. Make sure you use the correct WiX binaries (in other words WiX 4).
Linked Files?: I don't have any WiX 2 sources to migrate, but I am wondering if you have several source files that are interconnected. Was that even possible in WiX 2? I can't remember. In either case, I would make sure you have updated all WiX source files that are pulled in during the build process. Please read the log carefully. Maybe try to compile them with Candle.exe directly using the command line (cmd.exe instead of Visual Studio) to see if the file compiles OK.
Source Files?: If it still does not work, please put the source file online so we can have a peek. Github.com for example. A quick look at the source (the real McCoy) goes a long way sometimes - and sometimes it doesn't help at all. Maybe give it a go. Redacted sources are just fine - encouraged even. Please pay close attention to sensitive data: How do I avoid distributing sensitive information in my MSI by accident? (and this also goes for published source files - obviously - not just the compiled MSI and its helper files - such as silent installation template batch files).
In summary: That became a lot of babble. Maybe first try to compile the migrated WiX source with the right WiX 4 binaries to
determine if that works or not. Then work backwards to figure out what
happens during the build process.