Suddenly DeviceException on TWAIN Scan (log included)

[rwerg7w230jDF]

I'm suddenly encountering the following error when attempting to scan using TWAIN with the new DSM in NAPS2 Portable 8.2.1:

NAPS2.Scan.Exceptions.DeviceException: TWAIN error: Bummer

This issue appeared suddenly after a series of successful scans. Interestingly, another scanning application is able to use TWAIN without any problems at the same time, which suggests the scanner and TWAIN driver are functioning correctly.

Troubleshooting Attempts:

Restarting NAPS2 Portable does not resolve the issue.
The error persists even after multiple restarts and reattempts.

Observations:

The error seems isolated to NAPS2 Portable.
It’s unclear why the application cannot recover from this state, especially since other TWAIN-based applications work fine concurrently.

Request:
Could you help me understand what might be causing this error and how to recover from it?

System: Windows
Scanner: Canon R50
NAPS2 Version: 8.2.1 Portable archive (x64)

debuglog.txt

2025-10-06 09:46:51.0941 5040 Scanning with ScanDevice { Driver = Twain, ID = Canon R50 TWAIN, Name = Canon R50 TWAIN, IconUri = , ConnectionUri =  } 
2025-10-06 09:46:51.0941 5040 Scan source: Feeder; bit depth: Grayscale; dpi: 300; page size: 8.5x11 in 
2025-10-06 09:46:51.2585 20312 Debug: Using new dsm. 
2025-10-06 09:46:51.3300 20312 Using TWAIN DSM: C:\Users\john\AppData\Local\NAPS2\App\lib\_win32\twaindsm.dll 
2025-10-06 09:46:51.3300 20312 NAPS2.TW - Opening session 
2025-10-06 09:46:51.3300 20312 Debug: Thread 1: OpenManager. 
2025-10-06 09:46:51.3636 20312 NAPS2.TW - StateChanged (to 3) 
2025-10-06 09:46:51.3636 20312 Debug: Using TWAIN2 memory functions. 
2025-10-06 09:46:51.3636 20312 NAPS2.TW - Finding source 
2025-10-06 09:46:51.3636 20312 Debug: Source id = 1 
2025-10-06 09:46:51.3636 20312 NAPS2.TW - Opening source 
2025-10-06 09:46:51.3784 20312 NAPS2.TW - Name: Canon R50 TWAIN; Manu: Copyright CANON ELECTRONICS INC.; Family: R50 Driver; Version: 1.0 1.0; Protocol: 2.3 
2025-10-06 09:46:51.3784 20312 Debug: Thread 1: OpenSource. 
2025-10-06 09:46:52.1273 5040 Waiting for document timed out, returning 503 
2025-10-06 09:46:52.5590 20312 NAPS2.TW - Finishing with error NAPS2.Scan.Exceptions.DeviceException: TWAIN error: Bummer
   at void NAPS2.Scan.Internal.Twain.TwainScanRunner.Init()
2025-10-06 09:46:52.5929 20312 Debug: Thread 1: CloseManager. 
2025-10-06 09:46:52.5929 20312 NAPS2.TW - StateChanged (to 2) 
2025-10-06 09:46:54.1450 5040 ESCL server error waiting for document NAPS2.Scan.Exceptions.DeviceException: TWAIN error: Bummer
   at NAPS2.Scan.Internal.Twain.TwainScanRunner.Init()
--- End of stack trace from previous location ---
   at NAPS2.Scan.Internal.Twain.LocalTwainController.InternalScan(TwainDsm dsm, ScanOptions options, CancellationToken cancelToken, ITwainEvents twainEvents)
   at NAPS2.Scan.Internal.Twain.LocalTwainController.StartScan(ScanOptions options, ITwainEvents twainEvents, CancellationToken cancelToken)
   at NAPS2.Remoting.Worker.WorkerServiceImpl.TwainScan(TwainScanRequest request, IServerStreamWriter`1 responseStream, ServerCallContext context)
   at NAPS2.Remoting.RemotingHelper.HandleErrors(Error error)
   at NAPS2.Remoting.Worker.WorkerServiceAdapter.TwainScan(ScanOptions options, CancellationToken cancelToken, ITwainEvents twainEvents)
   at NAPS2.Scan.Internal.Twain.RemoteTwainController.StartScan(ScanOptions options, ITwainEvents twainEvents, CancellationToken cancelToken)
   at NAPS2.Scan.Internal.Twain.TwainScanDriver.<>c__DisplayClass4_0.<<Scan>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at NAPS2.Scan.Internal.RemoteScanController.Scan(ScanOptions options, CancellationToken cancelToken, IScanEvents scanEvents, Action`2 callback)
   at NAPS2.Scan.ScanController.<>c__DisplayClass15_1.<<Scan>g__DoScan|7>d.MoveNext()
--- End of stack trace from previous location ---
   at NAPS2.Scan.ScanController.<>c__DisplayClass15_0.<<Scan>b__6>d.MoveNext()
--- End of stack trace from previous location ---
   at NAPS2.Util.AsyncProducers.<>c__DisplayClass2_0`1.<<RunProducer>b__0>d.MoveNext()
   at async IAsyncEnumerable<T> NAPS2.Util.AsyncSink<T>.AsAsyncEnumerable()+MoveNext()
   at async Task<bool> NAPS2.Remoting.Server.ScanJob.WaitForNextDocument(CancellationToken cancelToken)+(?) => { }
   at async Task<bool> NAPS2.Remoting.Server.ScanJob.WaitForNextDocument(CancellationToken cancelToken)
   at async Task NAPS2.Escl.Server.EsclApiController.WaitForAndWriteNextDocument(JobInfo jobInfo)

[rwerg7w230jDF]

I suspect that the canon driver returns TWCC_BUMMER when NAPS2 calls https://github.com/soukoku/ntwain/blob/c5e296067843bafe39483390ddac1278b9b69048/src/NTwain/Triplets/DGControl/DGControl.Identity.cs#L79

• why would it do that suddenly, after it worked numerous times?

• Why can a different scanning app send the same message MSG_OPENDS to the driver and get success response? The only difference between the apps are the TW_IDENTITYs sent with the message. However, this should also reset after a restart. though NAPS2 comes with its own DSM...

• why would a restart of the scanner and PC not reset everything so that it works again?

[rwerg7w230jDF]

It started working again without me changing anything directly. All I did was:

1. Stopped sharing the scanner in the background and removed it from the list of shared devices.
2. Performed a successful standard TWAIN scan.
3. Re-shared the scanner , and now the eSCL-triggered TWAIN scan works as well.

However, I didn’t check whether the issue still existed before completing those steps , it’s possible that simply restarting the PC had already resolved it. But then again, why didn't a NAPS2 restart and logging out and in of Windows do it. Shouldn't the TWAIN states and everything be in memory only?!