Inventor: Error at start-up: The transaction manager failed to start

Question: 

Inventor fails to start with the following error message:   

Fatal error - no recovery possible
The transaction manager failed to start
Failed to create memory-mapped file used for scratch data. 

Answer: 

This may occur if there are restrictions or problems to write to the location defined for the "scratch data file".  By default, the location is: 

• "C:\Users\<USER NAME>\AppData\Local\Temp\"
  
  That location can be changed by modifying the registry key "C:\Program Files\Autodesk\Inventor 201X\Bin\Inventor.exe:ScratchDir", located in: 
• HKEY_CURRENT_USER\Software\Autodesk\Inventor\RegistryVersionXX.X\System\Preferences\Transactions\

The first thing to do is open the registry and browse to the key mentioned above.  Check access rights for the folder specified in the key and ensure the user has read and write permissions. 

If the key was modified and is pointing to a different location, change it back to the default folder ( "C:\Users\<USER NAME>\AppData\Local\Temp\") or to a folder the user can access. 

This error can also pop-up if the location of the 'Undo' folder is inaccessible.  Start inventor and go to the ribbon > Tools tab > Options panel > Application Options and select the ' File' tab.  Look for the path under 'Undo', which by default is "%USERPROFILE%\AppData\Local\Temp\" and ensure the folder exists locally and that the user has read/write access, otherwise, change the path to a different folder the user can access. 

https://knowledge.autodesk.com/support/inventor-products/troubleshooting/caas/sfdcarticles/sfdcarticles/Inventor-Error-at-start-up-The-transaction-manager-failed-to-start.html