See this TurboTax support FAQ if your license code is not working - https://ttlc.intuit.com/community/tax-topics/help/my-code-doesn-t-work/01/871966

i've triple checked and know the code is correct but stillget message tge code is invalid

Be on the lookout for an email from me for more information. Subject line is: TurboTax Activation Code
@joe_stella16 @bar21
@vin1 @fg2001gf 
@wagrieves 

I have now joined the 603 error crowd with no resolution in sight, even after spending 90+ minutes on the phone with 4 TurboTax reps, none of whom had ever heard of the problem. 

I installed TurboTax H&B 2019 on a single computer and seemingly successfully activated it, used it, printed some preliminary forms, saved my work, then shutdown my computer for the night.  The following day, after restarting my computer and launching TT 2019, I again had to activate.  This happened again the next day, so I contacted TT support.  Now, have gotten the 603 too many installations after being on the phone with no less than 4 representatives on December 26, being cut off (aka hung up on) twice by TurboTax, and downloading and installing a new copy from the TurboTax website.  Nothing works, and none of the 4 TurboTax reps I talked with had ever heard of the problem.

I have used TurboTax for at least 24 years.  Regarding this matter, I spent 90 minutes on the phone through 3 phone calls WITH NO RESOLUTION OF MY PROBLEM.  30 minutes with the first rep, who then said Advanced Technical Support wanted to talk with me directly and said she was transferring me to them...after a minute or two on hold, the person who answered the line was not Advanced Technical Support but another Program Support person WITH ABSOLUTELY NO KNOWLEDGE THAT I HAD ALREADY BEEN ON THE PHONE WITH TURBOTAX FOR 30 MINUTES.  After a fruitless 30 minutes with the second person, I was again put on hold, whereupon I was cut off (aka TurboTax hung up the phone).  NO RESOLUTION OF MY PROBLEM AFTER AN HOUR on this, my first call.  I called TurboTax back a few minutes after being hung up on, spent another 20 minutes with yet another rep, who when she put me on hold made a point of saying if we got cut off she would call me back and repeated the correct number.  Well, we got cut off, and I never received a call back.  I called a third time after trying installing a copy downloaded from the website.  At least he understood that at this point, there was not much else to try. Every rep I talked with said this was the first time they had heard of a user having this activation problem.  I had to direct them to this and other posts in the community.

I purchased TurboTax 2019 Home and Business off of Amazon. The product I ordered was a physical CD that was shipped by Amazon and was factory sealed with security tape.  I installed the software using the code on the package without issue.  After doing my Federal taxes it would not proceed to state.  It constantly prompted to download my state (Illinois) and after it downloaded it reports it's up to date.  When I clicked "Start State" the download process starts again.  I called Intuit/Turbo Tax support and after being on hold for 10 minutes I got a rude woman who after many minutes of trying everything I had already tried (uninstalling/reinstalling/etc) She asked me for my license code.  After verifying it with her 3 times she informed me that my license code was invalid.  I would have to go back to Amazon.  I returned the "defective" product to Amazon and they shipped me a replacement.  before proceeding I uninstalled the original installation and followed the online directions to "forcefully uninstall" the product.  I installed from the new CD and after running the program NEVER prompts for the License Key. I'm doing my taxes again.  Hope it works..  This is crazy.

Apparently TurboTax (Intuit) learned nothing from the last fiasco when they added poorly thought out DRM to their product. I had tons of issues that year and cancelled my auto  send authorization and used different products for as I recall 2 years until they saw the light and stopped this nonsense. Looks like it will happen again. I like the product but not enough to jump through hoops to use it or having them install malware on my machine. Goodbye.

My security code for Business version didn't work either.  Purchased and downloaded from Amazon on a Windows 10 PC.  I uninstalled and reinstalled and it still didn't work.  Out of frustration, I shut down my computer for the night and decided to deal with it this morning.  I again attempted to activate after the PC overnight shutdown and it worked!  My Business TT is activated! 

This error is caused by the Internet connection being unable to resolve connection to our server for license activation. There can be many reasons for this and they may not impact regular Internet usage and activity.

One of the following methods should resolve this issue. If they're successful, TurboTax will skip activation and open the starting screen where you can begin or continue your return.

If the product continues to prompt you for an activation code you have been unsuccessful.

Method 1: Temporarily disable your antivirus/anti-malware/firewall software

Method 2: Restart your router/modem

Method 3: Configure the TCP/IP settings

Method 4: IP config command line tool

I did...two call backs and still no resolve!  They even sent a new download.  Uninstalled the first one. Installed the new one ti no avail!  This is extremely frustrating. Been working on this for several hours now!!

Yes. I also have the same issue. After a windows update or TurboTax update, ask to enter the license code again. Then the code does not work any more.