The error "New scan found 1 MAC addresses, the existing record has 2. Check your SNMP and SSH connections." Basically just means that Lansweeper detected that a MAC address was removed from the device. Which it sees as a possible problem with the connection.
To remove the error you can blacklist the MAC address causing the issue. To do this you can do a test with devicetester.exe, which can be found in Program Files (x86)\Lansweeper\Actions on your Lansweeper server. Perform the test from your Lansweeper server to the problem machine, submit any relevant credentials.
By comparing the MAC address scanned and the two MAC addresses on your asset page, you can find the MAC address which is causing th error.
Just to be safe, I do recommend performing a database backup prior to running any scripts. Backup instructions can be found here: http://www.lansweeper.com/kb/94/backing-up-your-installation.html
Afterwards open DatabaseMaintenance.exe which can be found under Program Files (x86)\Lansweeper\Tools on your Lansweeper server or SQL Server Management Studio.
Copy/paste the script below and modify the highlighted code with the MAC address causing the issue, click Execute.
If you found multiple duplicate MAC addresses you can modify and run the script multiple times, once for each MAC address. Asset merging is usually caused by a single MAC address though.
INSERT INTO tsysMacBlacklist (Mac, Comment) VALUES ('AA:BB:CC:DD:EE:FF', 'Generic MAC')
GO
UPDATE tsysupdate SET MacBlacklist = GETDATE()