Check installed versions failed during upgrade

When upgrading to sql backup 5.4, all steps are successful except the check for installed version. I have verified that the old DLL is not loaded and a reboot of the server, where our installation of sql server resides, did not help.

tcp:10.25.14.10,3818: Server Component Installation - Failed
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Check installed versions - Failed

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The SQL Backup extended stored procedure DLL version is 5.1.0.2781, and 5.4.0.55 was expected.

[snip]

This operation completed successfully.