dotnet/wpf · error · FileFormatException

SR.XpsValidatingLoaderMoreThanOneThumbnailPart

Error message

SR.XpsValidatingLoaderMoreThanOneThumbnailPart

What it means

A FixedDocumentSequence, FixedDocument, or FixedPage part may have at most one Thumbnail relationship. ValidateRelationships counts thumbnail relationships on the part and throws FileFormatException when a second one is encountered.

Solutions

Delete redundant thumbnail relationships so each part has at most one.
Regenerate the thumbnail once and reuse the same relationship instead of adding new ones.
Enumerate and prune relationships with GetRelationshipsByType before saving/loading.
Rebuild the package with a compliant XPS writer.

Example fix

// before
foreach (var rel in part.GetRelationshipsByType(thumbRel).ToList())
    part.DeleteRelationship(rel.Id);
part.CreateRelationship(thumbUri, TargetMode.Internal, thumbRel); // still duplicates if others added elsewhere
// after
var existing = part.GetRelationshipsByType(thumbRel).ToList();
if (existing.Count == 0)
    part.CreateRelationship(thumbUri, TargetMode.Internal, thumbRel);

Defensive patterns

Strategy: validation

Validate before calling

var thumbRels = fixedPart.GetRelationshipsByType(thumbnailRel).ToList();
if (thumbRels.Count > 1)
    thumbRels.Skip(1).ToList().ForEach(r => fixedPart.DeleteRelationship(r.Id));

Type guard

static bool HasAtMostOneThumbnail(PackagePart part, string relType) =>
    !part.GetRelationshipsByType(relType).Cast<PackageRelationship>().Skip(1).Any();

Try / catch

try { loader.Load(packageStream); }
catch (FileFormatException ex) { // duplicate thumbnail rel: prune extras and reload
    PruneDuplicateThumbnailRels(packageStream); loader.Load(packageStream); }

Prevention

Regenerate thumbnails by updating the existing relationship rather than adding new ones.
When merging documents, de-duplicate thumbnail relationships per part.
Audit relationship counts after any package editing tool runs.

When it happens

Trigger: Opening an XPS package in which an FDS/FD/FP part carries two or more relationships of the XPS thumbnail type (http://schemas.microsoft.com/xps/2005/06/thumbnail); the count exceeds 1 during part.GetRelationshipsByType enumeration.

Common situations: Thumbnail generator utilities that add a new thumbnail without deleting the old relationship; document merge tools combining two documents each with their own thumbnail rel on the same part; manual OPC editing.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/bfad110d3287935c. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/FixedSchema.cs:572

                Uri targetUri = PackUriHelper.ResolvePartUri(partUri, rel.TargetUri);
                Uri absTargetUri = PackUriHelper.Create(packageUri, targetUri);

                PackagePart targetPart = package.GetPart(targetUri);

                if (!_printTicketContentType.AreTypeAndSubTypeEqual(new ContentType(targetPart.ContentType)))
                {
                    throw new FileFormatException(SR.XpsValidatingLoaderPrintTicketHasIncorrectType);
                }
            }

            checkRels = part.GetRelationshipsByType(_thumbnailRel);
            count = 0;
            foreach (PackageRelationship rel in checkRels)
            {
                count++;
                if (count > 1)
                {
                    throw new FileFormatException(SR.XpsValidatingLoaderMoreThanOneThumbnailPart);
                }

                // Also check for existence and type
                Uri targetUri = PackUriHelper.ResolvePartUri(partUri, rel.TargetUri);
                Uri absTargetUri = PackUriHelper.Create(packageUri, targetUri);

                PackagePart targetPart = package.GetPart(targetUri);

                if (!_jpgContentType.AreTypeAndSubTypeEqual(new ContentType(targetPart.ContentType)) &&
                    !_pngContentType.AreTypeAndSubTypeEqual(new ContentType(targetPart.ContentType)))
                {
                    throw new FileFormatException(SR.XpsValidatingLoaderThumbnailHasIncorrectType);
                }
            }

            // FixedDocument only has restricted font relationships
            if (_fixedDocumentContentType.AreTypeAndSubTypeEqual(mimeType))
            {

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