I have had an error code 6190-816 4 times in the last 8 weeks and I can't access my company files

I don't know what type of error you face while installation of QuickBooks but i share some of Intuit common error so choose the right one for you Links for installation errors . if still not able to get and need any technical help follow Intuit Tech Support .

Here, let me google that for you: https://community.intuit.com/articles/1265964-point-of-sale-error-an-internal-quickbooks-error-occurred-when-adding-customers-to-qb

Error Code: 51100 The WEP key for the Access Point you are attempting to connect to has changed since you last connected.
What to do: Verify the Access Point's WEP Key is entered correctly into the Nintendo DS. If your router has slots for more than one WEP key, the first (#1) must be the one selected on your router. If you need assistance, click here and select your router manufacturer and model number. If available, our router pages can provide specific steps and information that may help you with your router's WEP Key.
If you have multiple connection files saved to your Nintendo DS, the error message you received can help determine which connection file may be experiencing a problem:

• Errors ending in 0 = connection file 1
• Errors ending in 1 = connection file 2
• Errors ending in 2 = connection file 3
• Errors ending in 3 = Nintendo Wi-Fi USB Connector

Sometimes, you might experience a multi user-mode error and fixing that specific error occupies the highest priority.
Here QuickBooks Experts helps you to resolve this issue step-by ste. Contact 1-888-909-0535 or visit our link
How to Fix QuickBooks Error Code 3180 Call 1 888 909 0535 POS Help

1. Open the company file in QuickBooks Pro for Mac 2009.
2. Resort QuickBooks lists.
3. Run the Verify Data Utility.
4. Run the Rebuild Data Utility.
5. Create a Back Up of the file:

1. Go to the File menu.
2. Select Back Up to QuickBooks for Windows.
3. Save the file to the Desktop of the Mac.

6 Copy the file to a portable media.
7 On the PC, copy the file from the portable media to the Windows 8 Desktop.
8 Restore the backup into QuickBooks for Windows.

for more help visit QuickBooks Technical Support