You can find info about this problem here (on therion github page)
https://github.com/therion/therion/issues/510https://github.com/therion/therion/issues/502This problem is fixed in recent Therion compilation even in 6.3.1 (tested in my system some minute ago) BUT check which Therion version are you really using.
Therion is now compiled for 64 bit OS and will install in c:\program files instead of c:\program files (x86).
Check that cSurvey is using the lastest version from cSurvey settings and change path to the 64 bit folder (old x86 version can be removed).
You can also see which Therion version cSurvey still using in log panel during calculation.
If all is correct and Therion version is the lasted (or >6.2) I need to investigate the problem (so I need to see cSurvey log).
PS: the solution posted in the first link (proj-auto off in therion.ini) may work..actual cSurvey nightbuild work with custom therion.ini and you can add this options directly inside the survey (at now not fixed for computer)