Problem installing NetBeans 6.1 / Windows XP Pro SP2

Dear all, 

I’m trying to install this software with no success, earlier I had a previous version, version 5.  In the middle of the installation process I receive a message window (translated from Portuguese):

The installer is already in execution

It seems that another instance of the installer is already being executed.

It is not recommended that you run several instances of the installer at the same time.

Do you still want to run another instance of the installer?

<Yes> <No>

How to solve this?

Thank you,