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Error "An Unhandled exception occurred on the dispatcher thread".


Error "An Unhandled exception occurred on the dispatcher thread".

As a Mathcad User if you happen to receive an error message "An Unhandled exception occurred on the dispatcher thread. See “C:\ProgramData\PTC\MathcadPrime\Logs\MathcadPrime_Exception_###.log"



Than to address the problem, lets first understand the reason for this error followed by Resolution. 

Root Cause of Error:

  1. MathcadPrime.exe.config may have been corrupted
  2. User.config is corrupted for the user trying to launch Mathcad Prime

Resolution: There are two resolutions to address the problem

Resolution 1 -

1.  Rename the file MathcadPrime.exe.Config to old_MathcadPrime.exe.Config in the default Mathcad Installation location "C:\Program Data\PTC\Mathcad Prime".



2.  Rename the folder #PTC to old_PTC in the location " C:\Users\%username%\Appdata\Local"




3. Clear Temporary files on the Machine




If the above instructions fail to resolve the issue, uninstall the application, reboot the machine and reinstall Mathcad Prime


Resolution 2 -

  1. Alternate workaround is to copy Mathcad Prime Folder from the location C:\ProgramData\PTC from a machine on which Mathcad Prime is up and running and paste it to the same location on the machine having issue.
  2. If the former resolution does not solve the issue, uninstall the add-on Microsoft .Net Framework, download and re-install the local language version
  3. Uninstall and re-install Mathcad Prime






i tried all of them but didn`t work. I only got this error when i try to enter a number after this " := " .

Can someone help me ?

What version of Mathcad Prime and Windows OS are you using?



did you solve the problem in the meantime?


Dear Collegue!

I have tried these Resolution but nothing worked!
I have the MathCAD 8 express free version and I can´t open the .mcdx file.
Till today there werent any Problems opening the file.
And I am speechless because its a very important file to me and I need it for University.
I would be very thankfull if somebody could help me!!!

If somebody could convert it to pdf it would be enough for me.


In kind regards!


The Problem is I can neither open it nor convert to pdf but need the calculations ://

Edit: Luc Meekes fixed it for you here.
Edit 2: ...And in this thread, too!
It seems like there's something wrong with the file since I can't open it.




File location : C:\ProgramData\PTC\Mathcad Prime\Logs\MathcadPrime_Exception_20220512_084232.log

Build Number : 2022.03.01.001
System Culture : en-US; Current UI Culture : en-US
Architecture: x64
Application version is: PTC Mathcad Prime
Current license type is: Commercial


Exception data:
File being opened: C:\Users\danewman\Downloads\Neuberechnungen.mcdx
System.FormatException: Incorrect serialization format ---> System.Xml.XmlException: Name cannot begin with the '1' character, hexadecimal value 0x31. Line 1, position 13627.
at System.Xml.XmlTextReaderImpl.Throw(Exception e)
at System.Xml.XmlTextReaderImpl.ParseQName(Boolean isQName, Int32 startOffset, Int32& colonPos)
at System.Xml.XmlTextReaderImpl.ParseElement()
at System.Xml.XmlTextReaderImpl.ParseElementContent()
at System.Xml.XmlLoader.LoadNode(Boolean skipOverWhitespace)
at System.Xml.XmlLoader.LoadDocSequence(XmlDocument parentDoc)
at System.Xml.XmlDocument.Load(XmlReader reader)
at System.Xml.XmlDocument.Load(Stream inStream)
at Ptc.Controls.Core.Serialization.McdxDeserializer.Deserialize(Stream stream)
--- End of inner exception stack trace ---
at Ptc.Controls.Core.Serialization.McdxDeserializer.ThrowIncorrectSerializationFormatException(Exception ex)
at Ptc.Controls.Core.Serialization.McdxDeserializer.Deserialize(Stream stream)
at Ptc.Controls.EngineeringDocument.DeserializeWorksheetSection(PackagePart part, IWorksheetSectionPersistentData sectionData, IRegionCollectionSerializer regionCollectionSerializer, String fullFilePath)
at Ptc.Controls.EngineeringDocument.DeserializeWorksheetAndHeaderFooter(Package package, String fullFilePath)
at Ptc.Controls.EngineeringDocument.Read(Package package, FileLoadResult& result, String fullFilePath, Boolean newFromDocument)
at Ptc.Controls.EngineeringDocument.OpenPackage(FileLoadResult& result, String fileName, Boolean newFromDocument)
at Ptc.Controls.EngineeringDocument.OpenFileAndUpdateCWDState(String fileName)



MathcadPrime started at:
08:42:26 05/12/2022

I manage the Creo and PTC Mathcad YouTube channels for PTC, as well as all PTC Mathcad marketing in general.
23-Emerald III

Hi, Are you solve the ":=" problem?

Hi, yes, I did! I use a German version of Mathcad and I switched the language of my laptop to German, and it worked. I know that sounds silly but apparently the languages should match. I hope that works for you as well.

Thanks for sharing your solution to this issue.

i cant solve the problem , then i using Turkish language on my computer, so ı will try english version both, but i cant switch language mathcad.

What version of the program are you using?


Prime 8