Failed to mount database (hr=0x80004005, ec=1276)

Hi TomasHermansson,

This kind of errors are usually related to the log files and/or corrupted DB's. But I found a similar thread that may help you:

" 

Error:
Exchange is unable to mount the database that you specified. Specified database:
CONTOSOMBX\SG1\MB1; Error code: MapiExceptionCallFailed: Unable to mount database. (hr=0x80004005, ec=1276)

Cause

Interchanged Legacy Exchange DN of the Server and the MTA Object in Active Directory

Resolution

Open an Active Directory editor, such as ADSI Edit.
Expand Configuration [DomainName], and then expand, CN=Configuration,DC=DomainName,DC=DomainSuffix.
Expand CN=Services, and then expand CN=Microsoft Exchange.
Expand CN=OrganizationName, expand CN=Administrative Groups, and then expand CN=Exchange Administrative Group (FYDIBOHF23SPDLT).
Expand CN=Servers, select CN=ServerName, and click Properties.
Scroll down to legacyExchangeDN, select it, and click Edit. Make sure that the LegacyExchangeDN is of the format. "/o=OrganizationName/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=ServerName" and should NOT contain Microsoft MTA at the End.
Open an Active Directory editor, such as ADSI Edit.
Expand Configuration [DomainName], and then expand, CN=Configuration,DC=DomainName,DC=DomainSuffix.
Expand CN=Services, and then expand CN=Microsoft Exchange.
Expand CN=OrganizationName, expand CN=Administrative Groups, and then expand CN=Exchange Administrative Group (FYDIBOHF23SPDLT).
Expand CN=Servers, expand CN=ServerName, select CN=Microsoft MTA and click Properties.

Scroll down to legacyExchangeDN, select it, and click Edit. Make sure that the LegacyExchangeDN is of the format. "/o=OrganizationName/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=ServerName/cn=Microsoft MTA" and should contain Microsoft MTA at the End."

Source: https://social.technet.microsoft.com/Forums/lync/en-US/a7c79332-2a0a-419b-a987-ba67560c9d2e/recovery-database-error-hr0x80004005-ec1276?forum=exchange2010

For log files issues please also check: https://social.technet.microsoft.com/Forums/windows/en-US/4d1f1ec0-afa7-4a97-af2c-896f3d3c2abb/failed-to-mount-database-mailbox-database-hr0x80004005-ec528?forum=exchangesvravailabilityandisasterrecoverylegacy