In newer versions of TARGIT, InMemory is looking for a parameter called "licenseserver" in the targitdb.ini file to be able to validate the license. When upgrading InMemory, this parameter is not set automatically.
Add the parameter at the end of the targitdb.ini file found in C:\Program Files\TARGIT\TARGIT InMemoryDB\targitdb.ini like below, and then restart the server.
[general]
data_dir=C:\TARGIT\TARGIT InMemoryDB\Data\
log_dir=C:\TARGIT\TARGIT InMemoryDB\Log\
port=5060
password=password1234
licenseserver=https://[server name]:1301/