elsa-workflows/elsa-core · error · NotSupportedException

The BPMN continuation

Error message

The BPMN continuation '{evaluation.Continuation.GetType().Name}' is not supported by this host.

What it means

BpmnScopeHost.ApplyAsync switches over the interpreter's continuation types (Complete, Defer, Fault, …); any unrecognized continuation type falls into the default branch and throws NotSupportedException. Like the command applier's guard, this protects against version skew where a newer interpreter emits a continuation the host does not understand.

Solutions

Align all Elsa.Bpmn package versions so host and interpreter come from the same release.
If you defined a custom BpmnContinuation subclass, extend ApplyAsync's switch to handle it.
Rebuild the application after upgrading to avoid stale mixed assemblies.

Example fix

// before
<PackageReference Include="Elsa.Bpmn.Interpreter" Version="3.2.0" />
<PackageReference Include="Elsa.Bpmn.Hosting" Version="3.1.0" />
// after
<PackageReference Include="Elsa.Bpmn.Interpreter" Version="3.2.0" />
<PackageReference Include="Elsa.Bpmn.Hosting" Version="3.2.0" />

Defensive patterns

Strategy: try-catch

Try / catch

try { await host.EvaluateAsync(...); }
catch (NotSupportedException ex) when (ex.Message.StartsWith("The BPMN continuation")) { log.LogCritical(ex, "Version skew between interpreter and host"); throw; }

Prevention

Keep Elsa.Bpmn interpreter and host packages at identical versions.
Rebuild the app after upgrades to avoid stale assemblies.
Handle custom continuation types explicitly if you define them.

When it happens

Trigger: A BpmnEvaluation whose Continuation object is of a type added by a newer interpreter version than this BpmnScopeHost supports (mixed package versions).

Common situations: Partially upgraded Elsa.Bpmn packages where the interpreter DLL is newer than the hosting DLL; custom continuations introduced by an extension the host does not handle.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/4b1ae38d1d8f1c18. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Bpmn/Hosting/BpmnScopeHost.cs:219

            await ApplyAsync(memory, evaluation);
        });

    private async ValueTask ApplyAsync(BpmnScopeMemory memory, BpmnEvaluation evaluation)
    {
        await new BpmnCommandApplier(_context, _process, memory).ApplyAsync(evaluation.Commands);

        switch (evaluation.Continuation)
        {
            case BpmnContinuation.Complete complete:
                // The scope completes because the interpreter said so, never because it ran out of children.
                await _context.CompleteActivityAsync(new Outcomes(complete.Outcome));
                break;
            case BpmnContinuation.Defer:
                break;
            case BpmnContinuation.Fault fault:
                throw new BpmnScopeFaultException(fault.Code, fault.Message);
            default:
                throw new NotSupportedException($"The BPMN continuation '{evaluation.Continuation.GetType().Name}' is not supported by this host.");
        }
    }

    /// <summary>
    /// Projects every diagnostic the interpreter has appended since the last evaluation onto this scope's own
    /// execution log, keyed by element id. Under Option A only bound work has an activity id, so a gateway, an
    /// intermediate event or a sequence flow has nothing else in the journal to say where a token went; this is
    /// write-only and never read back by the interpreter or this host.
    /// </summary>
    /// <remarks>
    /// Runs on <see cref="_context"/> — this scope's own context — and never a child's: the diagnostic describes
    /// this scope's decision about a child, and the child may already be torn down by the time this runs. Called
    /// with the evaluation's own <see cref="BpmnEvaluation.State"/>, before <c>Prune()</c> caps
    /// <see cref="BpmnExecutionState.Diagnostics"/> at 200 entries, because projecting from what was actually
    /// persisted would lose whatever pruning already dropped. The last diagnostic id it has projected is kept in
    /// <see cref="BpmnScopeMemory.DiagnosticsCursorPropertyKey"/> so a resumed scope does not re-emit one a
    /// previous evaluation already turned into a journal entry.
    /// </remarks>

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