When searching for a term in MultiTerm Desktop 2017, the following error is thrown:
The entry in the termbase causing this issue, if known, will no longer be editable or displayable.

Solution 1: Update MultiTerm 2017 to the latest version

This issue was fixed in MultiTerm 2017 CU06. You can update your software to the latest version by using the installer here. Please also be aware that MultiTerm 2017 has reached end of life on January 31, 2021. 

Solution 2: Recreate the termbase

The following article explains How to create a termbase from a termbase definition (XDT) and termbase data (XML) file in MultiTerm.
In this case it is essential that data is imported using MultiTerm Desktop 2017 (even for MultiTerm Server 2015 termbases). Importing the data in MultiTerm 2015 will not fix the corruption.

Note: The corrupted entries will be discarded in this process.

Workaround:

To prevent this issue from occurring in the first place either:

• Set the termbase layout to Default layout in Home > Display before merging entries during entry creation

Or

• Do not merge entries during creation, but instead create the new entry first and merge them afterwards.

Entries were merged during the creation of an entry, while the termbase layout was not set to "Default layout".

This problem was due to an issue in MultiTerm 2017. A fix was implemented in MultiTerm 2017 CU06.