dotnet/wpf · error · ArgumentException

FileAccess value is not valid.

Error message

FileAccess value is not valid.

What it means

After checking for ReadWrite and Write access, UpdateModeFlagFromFileAccess throws ArgumentException (SR.FileAccessInvalid) if the FileAccess value does not include the Read bit, i.e. it is not a recognized FileAccess combination (0, or an out-of-range value).

Solutions

1. Pass FileAccess.Read, FileAccess.Write, or FileAccess.ReadWrite
2. Initialize the FileAccess variable properly before use
3. Validate the access value from config/deserialization before passing it

Example fix

// before
FileAccess access = 0;
OpenCompoundFile(stream, access);
// after
FileAccess access = FileAccess.Read;
OpenCompoundFile(stream, access);

if (access != FileAccess.Read && access != FileAccess.Write && access != FileAccess.ReadWrite) throw new ArgumentException("Invalid FileAccess", nameof(access));

static bool IsValidFileAccess(FileAccess a) => a == FileAccess.Read || a == FileAccess.Write || a == FileAccess.ReadWrite;

try { OpenContainer(stream, access); } catch (ArgumentException ex) when (ex.ParamName == null && ex.Message.Contains("FileAccess")) { /* fix access value */ }

When it happens

Trigger: Calling a compound-file open/create API with a FileAccess value of 0 (FileAccess.None) or an invalid casted integer.

Common situations: FileAccess field defaulted to 0, uninitialized variable, or an invalid value deserialized from config/state.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

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AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/9bc458ae6b7f68a8. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/MS/Internal/IO/Packaging/CompoundFile/NativeCompoundFileAPIs.cs:47

            //  cost/benefit ratio.
            if( FileAccess.Write == access )
                throw new NotSupportedException(
                    SR.WriteOnlyUnsupported);
            
            // Generate STGM from FileAccess
            // STGM_READ is 0x00, so it's "by default"
            if( (  FileAccess.ReadWrite                == (access &  FileAccess.ReadWrite) )  ||
                ( (FileAccess.Read | FileAccess.Write) == (access & (FileAccess.Read | FileAccess.Write))) )
            {
                grfMode |= SafeNativeCompoundFileConstants.STGM_READWRITE;
            }
            else if( FileAccess.Write == (access & FileAccess.Write) )
            {
                grfMode |= SafeNativeCompoundFileConstants.STGM_WRITE;
            }
            else if( FileAccess.Read != (access & FileAccess.Read))
            {
                throw new ArgumentException(
                    SR.FileAccessInvalid);
            }
        }

        internal static int SafeStgCreateDocfileOnStream(
            Stream s,
            int grfMode,
            out IStorage ppstgOpen
            )
        {

            Invariant.Assert(s != null, "s cannot be null");

            UnsafeNativeCompoundFileMethods.UnsafeNativeIStorage storage;
            UnsafeNativeCompoundFileMethods.UnsafeLockBytesOnStream lockByteStream = new UnsafeNativeCompoundFileMethods.UnsafeLockBytesOnStream(s);
            int result;

            result = UnsafeNativeCompoundFileMethods.StgCreateDocfileOnILockBytes(

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