Project fails to load after VB6 upgrade wizard: re-run conversion or restore the pre-upgrade baseline?

Question

Failed upgrade leaves a partially converted project

A VB6 project processed by the Visual Studio Upgrade Wizard can end up in a mixed state: a new .vbproj exists, but it fails to load or build in the target IDE, while some source files were converted and others were not. The documented failure condition here is the project file being reported as incompatible or corrupted at load time, though the exact error text varies by Visual Studio version and should be recorded from the Output or Error List window in the failing environment rather than assumed.

Constraints

A pre-upgrade snapshot exists (source control commit plus a full directory copy), and the original VB6 environment can still rebuild the baseline. The concern is that continuing development on the partially upgraded output risks hidden inconsistencies, since it is not always clear which files the wizard modified. Third-party COM references may also fail independently of the code conversion, complicating diagnosis.

Open questions

After a partial conversion, should recovery always restore the pre-upgrade baseline and re-run the wizard, or is manual repair of the partial output ever the safer option?
What verification (clean rebuild after deleting bin/obj, comparison against baseline behavior) is sufficient to confirm the recovered project is trustworthy?
Does the IDE version used for the re-run change the outcome, given that project schemas and default target frameworks differ across Visual Studio versions?

Tasadduq Burney · Answer

Answer: restore the pre‑upgrade baseline and re‑run the wizard
When the Visual Studio Upgrade Wizard leaves a project in a partially converted state, the safest recovery is to return to the known‑good VB6 baseline and run the wizard again in a clean IDE instance.
Why this works (likely explanation)
The wizard stops when it encounters unsupported VB6 syntax, missing COM references, or conversion errors. It writes a .vbproj file that references a mix of converted and unconverted source files, which the target IDE treats as incompatible or corrupted. Restoring the baseline guarantees that every file is in its original, unchanged state before the wizard attempts the conversion again.
Steps to recover

Restore the baseline: checkout the pre‑upgrade commit or copy the saved directory back over the working tree.
Start a clean IDE instance: close any open solutions, then open Visual Studio (the same version you intend to target) with no loaded projects.
Run the Upgrade Wizard: point it at the restored VB6 project file. Let it run to completion, noting every error or warning it reports in the Output or Error List window.
Address wizard‑reported issues: fix each reported problem (e.g., add missing COM references, replace unsupported API calls) before allowing the wizard to finish.
Clean build artifacts: delete the bin and obj folders for the project.
Perform a clean build: build the solution and verify that it completes with zero errors and zero warnings.
Verify functional equivalence: run the application’s test suite or a known‑good scenario and compare its output to the baseline build’s behavior.
Optional diff check: use a file‑diff tool to confirm that only the files listed in the wizard’s conversion report have changed relative to the baseline.

When manual repair might be considered
Only if the wizard’s error log shows a single, isolated, non‑critical issue (for example, one unsupported API call) and you have verified that all converted files compile and behave identically to the baseline should you attempt to manually edit the partial output. In all other cases, hidden inconsistencies remain a risk, so restoring the baseline is recommended.
Missing diagnostic detail
To confirm that the wizard’s failure is due to conversion errors rather than, for example, a corrupted IDE installation, please provide the exact error text shown in the Output or Error List window when the project fails to load.

Project fails to load after VB6 upgrade wizard: re-run conversion or restore the pre-upgrade baseline?

Failed upgrade leaves a partially converted project

Constraints

Open questions

1 answer

Answer: restore the pre‑upgrade baseline and re‑run the wizard

Why this works (likely explanation)

Steps to recover

When manual repair might be considered

Missing diagnostic detail

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