Using SCM command-line tools as part of an RTC build

We have an automated build that has the following characteristics:
1 - we use the integrated scheduling to schedule an automated build;
2 - we accept some inputs from a 3rd party source, that we want to automatically deliver into SCM as part of the build procedure.

I have found references, and have manually executed an SCM checkin and SCM deliver operation from the command line
(See https://jazz.net/forums/viewtopic.php?t=2482&highlight=ant+task+checkin+deliver)

Where it implies that "You should be able to use the command line client to check-in / deliver the artifacts during the build."

I access the scm command line using an Ant "exec" task.

However, I keep getting the following error on both our build server and locally if I try to run the Ant target directly from RTC:

Could not initialize data area:
Another RCP application is running in this local workspace. File locked at file: C:\_workspace

This seems to imply that I cannot call "scm" to do work while either the build server or my local RTC are running.

Has anybody successfully invoked (via "ant exec") "scm" from within an automated build are directly from withing RTC? Would you be willing to share your technique?

Thanks in advance