The file extension LCK is used by various programs for so-called Program Lock files. These files are used to restrict access to other files, such as a database, to one user at a time. Usually, this file will be automatically opened with the appropriate protected file, and then it will be locked so that if another user attempts to open the protected file, it will be denied.
Programs that use LCK files include Microsoft SharePoint Designer, Corel Paradox, Pegasus Mail, and Skype.
Of course these files are not compatible with each other and should neither be opened nor moved from their directory or deleted.
Most often resolving problems with opening LCK files is very simple. Just install an appropriate program that supports such files. All of the listed programs support LCK files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of LCK files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate LCK files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Referenced by various applications applications is not on the list, select "Browse" option in order to manually locate the directory where Referenced by various applications has been installed.
Sometimes problems with opening LCK files may not lie with the application itself, but can arise due to other causes, such as: