VS .NET 2003 solution: Building non-existing configuration with empty name

[ASolovey]

I have VBP 5.6 installed. In the build script I have a step that builds single configuration (Release) of VS .NET 2003 solution.
It works fine in most cases. But sometimes, after solution is changed (projects added, or something - I haven't figured any regularity), VBP begins building it wrongly. After successfull building of Release configuration it immediately attempts to build one more configuration with empty name (which of course does not exist).

It displays the following:
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Building configuration ''...
Command: "C:\Program Files\Microsoft Visual Studio .NET 2003\Common7\IDE\devenv.com" D:\BuildRoot\PROGRAM\MyProject\REL_1.0.1\BUILD\WOR K\SOURCE\MyProject.sln /build
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VS7 of course says that the command line is invalid, configuration name is missing.
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Invalid solution configuration

Usage:
devenv [solutionfile | projectfile | anyfile.ext] [switches]
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I have upgraded VBP up to 5.7. It didn't help.
Nothing helps in this situation except re-creating the solution from scratch.
Is it a well known issue?
Can you help us to resolve it?
How should we approach it?

Thanks in advance.