Launching Pro Tools 6.x on Windows XP, it gave: An error (-1) occurred while initializing OMS you may continue without OMS functionality.

This is a known problem caused by having a Yamaha USB MIDI interface or MIDI keyboard installed into Windows XP. Currently, the only fix for this is removing the Yamaha interface from your system, uninstalling the software, manually removing the registry entries, and repairing Pro Tools.

First of all make sure you are using Pro Tools LE v6.1.1 or higher, because the MIDI port problem can occur in v6.1 as a bug without having installed the Yamaha software.
There are known issues that can cause problems for Pro Tools when Yamaha software for a Motif or other Yamaha products has been installed on a Windows PC. (Yamaha USB products such as a Motif, DM2000, or P120 Piano).
Symptoms:

1) This software can cause the MIDI ports on the Digi 001 or Digi 002 or Digi 002 Rack not to show up in a Pro Tools session (Pro Tools LE 6.1.1).

2) And/or it can cause an error message when launching Pro Tools:
An error (-1 ) occurred while initializing OMS you may continue without OMS functionality. (Abase # 27250)

3) And/or it can cause the launch of Pro Tools not to finish and revert back to the desktop. (Abase # 27045)

4) Yamaha Motif USB may also cause communication problems with control surfaces including the Command|8.

The solution below may prevent users from having to backup the system drive and reinitialize it, since just removing the Yamaha software from Add/Remove Programs has not fixed this issue in the past.
Some customers have used registry cleaner software (they have purchased) to manually remove the driver files associated with the Yamaha software. These registry cleaning applications cost around $20.00. (Registry First Aid or Registrar)
There is also a shareware (free) application called, RegCleaner that may also do the trick, although we have not tried it. Consequently, RegCleaner would be worth trying before purchasing the same type of registry cleaning software, to possibly save money. Here is a link to download RegCleaner:
http://worldstart.com/weekly-download/archives/reg-cleaner4.3.htm

Only delete files specified below, otherwise, you can cause problems to Pro Tools and/or other applications. Creating a system restore point in XP is also a good idea, just in case you make a mistake. (Start menu > All Programs > Accessories > System Restore).

How to remove the Yamaha driver files:
1) Launch your registry cleaning application (RegCleaner, Registry First Aid or Registrar). Search for the files in the registry editor and delete them. (Do NOT delete any other files)
Files to search for and delete: ymidusb.sys
xgusb.cpl
xgusb.inf
2) Repair Pro Tools from Add/Remove Programs. Start Menu > Control Panel > Add/Remove Programs. Select Digidesign Pro Tools LE and click Change/Remove. Then select the Repair button and proceed with the prompts.

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