microsoft/autogen · error · ArgumentException

The number of elements in the source is greater than the ava

Error message

The number of elements in the source is greater than the available space from arrayIndex to the end of the destination array.

What it means

Capacity check in ICollection<AIContent>.CopyTo: throws ArgumentException when array.Length - arrayIndex < Content.Count, i.e. the remaining space from arrayIndex to the end cannot hold every AIContent item in the source collection.

Source

Thrown at dotnet/src/Microsoft.AutoGen/AgentChat/Abstractions/Messages.cs:331

        return this.Content.Any(x => x.AIContent == item);
    }

    /// <inheritdoc cref="ICollection{AIContent}.CopyTo" />
    public void CopyTo(AIContent[] array, int arrayIndex)
    {
        if (array == null)
        {
            throw new ArgumentNullException(nameof(array));
        }

        if (arrayIndex < 0 || arrayIndex >= array.Length)
        {
            throw new ArgumentOutOfRangeException(nameof(arrayIndex));
        }

        if (array.Length - arrayIndex < this.Content.Count)
        {
            throw new ArgumentException("The number of elements in the source is greater than the available space from arrayIndex to the end of the destination array.");
        }

        for (var i = 0; i < this.Content.Count; i++)
        {
            array[arrayIndex + i] = this.Content[i].AIContent;
        }
    }

    /// <inheritdoc cref="IEnumerable{AIContent}.GetEnumerator" />
    public IEnumerator<AIContent> GetEnumerator()
    {
        return this.Content.Select(x => x.AIContent).GetEnumerator();
    }

    /// <inheritdoc cref="IList{AIContent}.IndexOf" />
    public int IndexOf(AIContent item)
    {
        return this.Content.FindIndex(x => x.AIContent == item);

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Size the destination to at least arrayIndex + source.Content.Count
2. Allocate fresh per copy: var a = new AIContent[msg.Content.Count]; msg.Content.CopyTo(a, 0);
3. When merging into a shared buffer, track the running offset and grow the buffer when remaining space is insufficient

Example fix

// before
var dest = new AIContent[msg.Content.Count];
msg.Content.CopyTo(dest, 1); // 1..end holds Count-1 slots < Count
// after
var dest = new AIContent[msg.Content.Count + 1];
msg.Content.CopyTo(dest, 1);

if (array.Length - arrayIndex < msg.Content.Count) Array.Resize(ref array, arrayIndex + msg.Content.Count);
msg.Content.CopyTo(array, arrayIndex);

When it happens

Trigger: Calling CopyTo with an array exactly Content.Count long but a non-zero arrayIndex; sizing the destination from the wrong count (e.g. another message's Count) before copying.

Common situations: Reusing a buffer sized to a previous, smaller message; off-by-one in capacity math (array.Length - arrayIndex miscomputed); copying several messages into one array while accumulating the index but not the total size.

Related errors

• Value cannot be null. (Parameter 'array')
• Specified argument was out of the range of valid values. (Pa
• The recent update is not a TextMessage
• The content has more than one choice. Please try another inp
• Invalid ChatResponseMessage

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/235af8bdbe88ed38. Report an issue: GitHub.