I can't Open two quickbooks Company in one time.

For complete QuickBooks 2002 Manual downloads follow http://support.quickbooks.intuit.com/archive/index/ndxw_10_updates2.html.

Intuit recommends 2 solutions for this problem. The first solution may solve your problem, or you may need to try both to resolve the issue. For best results, perform the solutions in the order shown.

Solution 1: Download QuickBooks File Doctor

Download, install and run the QuickBooks File Doctor.
If you see No problem detected in your Company File, and you still experience the issue, go to solution 2.
Solution 2: Check for data damage.

Perform the standard data damage troubleshooting.

for more help visit
QuickBooks 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

If you have two QUICKBOOKS pro LICENSES you can access the same file from two computers. You will not be able to open the same account of each file ex same client. Verify that you are under multiuser under "file".
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Hi there,

1. Open the QuickBooks sample company and try to print the same form or type of form. If it prints successfully, your company data, form template, or customized report may be damaged.
2. Reopen your company file and try to print an uncustomized (standard/default) form template or non-memorized report. If the issue occurs again, refer to Verifying and rebuilding the QuickBooks company data and then attempt to print again.
3. If you were printing a batch of forms in QuickBooks, attempt to print a single form. If successful, try printing smaller batches.
4. If you were able to print from QuickBooks in the past from this company file:
5. Turn off the printer, restart your computer, and then turn the printer back on.
6. In QuickBooks, choose File > Printer Setup and check the printer settings for the specific form you're trying to print.
7. Click Help in this area for more detailed instructions on these settings.
8. Ensure that you have the latest printer drivers for your printer. Go to the manufacturer's website to download and install the most current drivers.
9. Replace the QuickBooks Qbprint.qbp file:
10. Close QuickBooks.
11. Rename the qbprint.qbp file.
12. Open QuickBooks and attempt to print again.
13. If the issue persists, repair the QuickBooks installation.

You will need to verify and rebuild your data file. Please follow the steps i provided, this will guide you threw the process.

Verify your data:

1. Close and reopen QuickBooks to create a new Qbwin.log file.
2. Choose Window > Close All, so that no company files or QuickBooks windows are open.
3. Choose File > Utilities > Verify Data.
* If you see QuickBooks detected no problems with your data, your data is clean. Click OK.
* If you see Your data has lost integrity, your data file is damaged. Run the Rebuild Data utility to repair the damage. You may need to run Rebuild two or more times to repair all of the damage. Rerun the Verify Data utility after each rebuild to verify that the errors have been corrected.
* If your see A data problem prevents QuickBooks from continuing, then your data file has a structural problem. Run the Rebuild Data utility to repair the damage.

Rebuild your data:

Important: If the company file is on a network drive, copy the file to a local computer before attempting to run this utility. Be prepared for this computer to be unavailable for several hours running the Rebuild utility. Never rebuild or update a company data file that is located on a remote drive (for example, by accessing it over your network).

If you can't open QuickBooks to run the Rebuild Data utility refer to QuickBooks does not open.

If you're unable to open your company file when double-clicking your QuickBooks desktop icon, see Opening QuickBooks when troubleshooting.

To rebuild the file:

1. Choose Window > Close All.
2. Choose File > Utilities > Rebuild Data.
3. Click OK to the warning message requiring a backup of the company file before starting the rebuild.

Important: Do not replace your current backup. Intuit recommends using a newly formatted external media source for this backup (such as a CD or DVD). If necessary, back up to your local hard drive.
If a message appears asking if you want to replace the backup file, click No.
To avoid overwriting the current file, enter a new name in the Filename field.

4. At the bottom of the QuickBooks Backup window, click OK.

Important: If the backup process fails, at the Rebuild prompt, click Cancel.
Do not continue the Rebuild process with your original company file if the back up process does not complete successfully. This can lead to permanent data loss.
You must make a copy of the company file and attempt the Rebuild process again using the copy of the company file.
Rename the copy of the company file with a unique name to avoid confusion with the original file.

5. The Rebuild Data utility starts as soon as the backup process completes. Click OK to the Rebuild has completed message.
6. Close the company file, and then reopen it to refresh the lists in the file:
1. Choose File > Close Company.
2. Open the company file:
* QuickBooks 2008 and 2007: Choose File > Open or Restore Company. Then select Open a company file and click Next.
* QuickBooks 2006: Choose File > Open Company.
7. Click the company file, and click Open.
8. Run the Verify Data utility.

Neither of these programs should EVER allow more than one company file to open at time. Each Company file operates as a seperate database.