Q: I'm using GXInstallQDTranslator to turn all my QuickDraw calls into GX Shapes, and the like. As far as I can tell, this works fine, and when I'm done, I call GXRemoveQDTranslator, but it returns an error code of -51, which isn't mentioned in any of the GX Printing documentation I have. What's happening?

A: When there is a -51 or -39 error from within an application using GX, it is usually caused by double disposing a GX object (e.g., a shape, ink, style, or transform).

The -51 error is generated because the shape is located in the disk-based backing-store file. After the first dispose, the backing-store file is deleted (as it should be), but after the second dispose, the shape's backing-store file is gone, so the file manager returns a -51= rfNumErr (reference number invalid) error.

Make sure you're not disposing of the GX shape created in your QDTranslator handler. Contrary to the sample code on page 1-22 of Inside Macintosh: QuickDraw GX Environment & Utilities, GX does dispose of the shape for you.

If this doesn't solve the problem, install the "GXGraphics (debug) init" and turn on validation to make it easier to find the origin of the double-dispose. Start with the following validation setting:

    GXSetValidation (gxPublicValidation + gxTypeValidation)

If your application continues to run without any validation errors from GX, turn up validation by adding the following flag:

    gxAllObjectValidation

    gxApBlockValidation + gxApHeapValidation.

If everything continues to work, add the following flag to the mix:

    gxCheckApHeapValidation

As you increase the amount of validation, you'll see an increasing slowdown, but hopefully, validation will catch the problem.

For additional details about GX validation, see the chapter on GX validation in GX Environment & Utilities.

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