---
title: "A device attached to the system is not functioning"
canonical: "https://support.soteria-cloud.co.za/space/SCKB/50167828/A%20device%20attached%20to%20the%20system%20is%20not%20functioning"
format: markdown
---
## Symptoms

Backup fails with the error: **"A device attached to the system is not functioning."**

## Troubleshooting Steps

### Step 1: Check Volume Tracker Logs

Check the **Volume tracker logs** located in:

```
C:\ProgramData\Acronis\VolumeTrackerLogs
```

### Step 2: Identify the Error Code

Look for one of the following error codes in the logs:

- `0x235000b` = VOLUME_LOCK_NOT_DETECTED → Follow Solution 1
- `0x235001f` = VOLUME_SNAPSHOT_FILTER_NOT_FOUND → Follow Solution 1 or Solution 2

## Solution 1: Restart and Disable CBT

1. Restart the machine after the backup failure
2. Disable [Changed Block Tracking (CBT)](https://www.acronis.com/en-us/support/documentation/CyberProtectionService/#changed-block-tracking.html) on the affected machine
3. Retry the backup

## Solution 2: Registry Fix

> ❌ **Warning:** Editing the Windows Registry can cause system issues if done incorrectly. Proceed with caution and create a registry backup before making changes.

### Steps

1. Open **Windows Registry Editor**: Click **Start**, search for `regedit.exe`, and press Enter
2. Navigate to:  

`HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{533c5b84-ec70-11d2-9505-00c04f79deaf}`
3. Check if `fltsrv` is present in the `UpperFilters` value
4. If `fltsrv` is missing, add this data to the value
5. Restart the machine and retry the backup

> ✅ If the issue persists after trying both solutions, contact Soteria support for further assistance.