Error 1001. The specified service already exists

This message can come up if you install a newer version of for example JTB FlexReport. The solution is to first uninstall.

If there is a problem to uninstall. Make sure you have administrator rights.
Stop the JTB FlexReport service(s). The name of the services(s) can be “JTB FlexReport”, “JTB FlexReport Service”, “JTB FlexReport Core Service”, “JTB FlexReport Chart Service”, JTB FlexReport Sampling Service”, “JTB FlexReport Auto Chart Service”.
You can also try the hard way:
Run cmd.exe with enough user rights
net stop "JTB FlexReport"
sc delete "JTB FlexReport"

Now try to uninstall. It might also be needed to restart the server before running the setup again.

In this example it is "JTB FlexReport Service".
Stop the service in Windows Services.
Using the registry:
1. Run REGEDIT.EXE.
2. Find "HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services" and locate the service and delete the key.
Using command line (as administrator):
NET STOP "JTB FlexReport Service"
SC DELETE "JTB FlexReport Service"
Delete the installation folder.
Locate JTB FlexReport in the registry under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall
or
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\
   Microsoft\Windows\CurrentVersion\Uninstall
You can do a Find and then delete that key.
It might be named like this: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\
   Microsoft\Windows\CurrentVersion\
   Uninstall\{1015F883-967B-4E57-B6C3-6923A1186A24}
Now try to install.
Restart if needed.

See also Error 1001 The specified service does not exist as an installed service