Failed to verify document Trados Studio 2014, 2015

At the attempt to do a “verify” on a specific file, not on all files, the following message is issued:

“Failed to verify document: The process failed to access the file ‘XYZ.xml’ because it is being ued by another process”

SW configuration:

64-bit operating system

Windows 7 Professional, Service Pack 1

SDL Trados Studio 2014 Freelance

(SDL Trados Studio 2014 SP2 – 11.2.4422.11)

As well as with

SDL Trados Studio 2015 Freelance

(SDL Trados Studio 2015 – 12.0.4996.3)

HW configuration:

Intel Core i7-4770 CPU @ 3.40GHz

32 GB RAM

How can this be addressed?

thanks