The robot uses webdriver procotol to drive browsers. And to control a browser, the robot uses different drivers for each browser. Chrome has chromedriver, Firefox has geckodriver, Edge has edgedriver etc.
There are multiple reasons you may be getting this error, so we will go through all of them here and we assume you are using Chrome for your automations. Since that is our recommended browser in your flows anyway. 
1. User Data Dir
Chrome browser has a feature called user-data-dir that lets you separate sessions from each other and also keep all the previous session info in different folders.
You can start chrome with --user-data-dir property like this
google-chrome --user-data-dir=C:\project-x-chrome
All the history, installed extensions and session info will be kept here from the opened browser session until you close it. If you give the same path again with this parameter and open Chrome again, it will continue from the previous session.
Your default chrome browser even works like this. It uses a default user data dir directory every time you open it. The Chrome user data dire default locations can be found here: User Data Directory
There is just one catch! You canât open two chrome instances that use the same directory. Chrome will not start at all.
And this may be the main reason, you are getting this error in Robomotion.
If you do not provide a path to âOpen Browserâ User Data Dir property, chromedriver manages this by generating a temporary path for every Chrome session.
But if you provide a âUser Data Dirâ to Open Browser, then for every Open Link you should use âSame Tabâ checkbox. If you do not do that, then a new window session will start that will try to use the same User Data Dir and you will get this error.
This wonât happen if you do not set âUser Data Dirâ in Open Browser, since every new Chrome window session will get its own tmp dir.
But if you want âNew Windowâ + âUser Data Dirâ at the same time, then for every New Window with âOpen Linkâ you should use an âOpen Browserâ with a different User Data Dir (or none) before the âOpen Linkâ node.
2. There is no chromedriver on your machine
You need chromedriver.exe (Windows) or chromedriver binary (Mac and Linux) on your machine to drive Chrome Browser. You actually do NOT need to do anything here, the robot downloads and manages the right version needed for your Chrome.
But it is always a good idea to check if this binary exists on your system to make sure everything is in place. For Windows, the binary should be under %LOCALAPPDATA%/Robomotion/bin directory, for Linux and Mac it should be under $HOME/.config/robomotion/bin
3. Your chromedriver and Chrome versions do not match
Again the robot should handle this and should manage the right version downloads for you, but you can also check this one.
Open command prompt on Windows or Terminal on Linux/Mac
and run %LOCALAPPDATA%/Robomotion/bin/chromedriver --version command on Windows and $HOME/.config/robomotion/bin/chromedriver --version command on Linux/Mac, the output should be something like this:
~ $HOME/.config/robomotion/bin/chromedriver --version
ChromeDriver 98.0.4758.80 (7f0488e8ba0d8e019187c6325a16c29d9b7f4989-refs/branch-heads/4758@{#972})
and then run google-chrome --version command, the output should be something like this:
â ~ google-chrome --version
Google Chrome 98.0.4758.80
The major versions should be same or chromedriver will not work, here we see the major versions are the same: 98.x.y.z
4. Not using Stable version but instead using a Beta or Canary version of Chrome
Robot or the chromedriver expects google-chrome binary on your system. The beta and canary version binaries are named differently. We only support the stable version of Browsers.
Download the latest stable Chrome version from Google Chrome - Download the Fast, Secure Browser from Google
5. Linux without a Desktop Environment
If you installed your Robot into a Linux machine where it does not have a Desktop. You are probably connecting to this machine via SSH. So you canât expect a Chrome browser to open in a Desktopless environment. 
But there is a way to do this actually, and that is called a Headless Browser session. It is easy to set up. Just go to the âOpen Browserâ node properties in your flow and select âHeadless Chromeâ from the list. Thats it!
So these are the cases for troubleshooting this error. If you are still getting this error, that would be another case we have missed, just reach out to us from this page or through our https://community.robomotion.io Discord community server.