Pass the LabTalk string variable in quotes and then use LT_get_str to read it. The following snippet should help you.
LabTalk.Ini.File$ = strIniFile;
LabTalk.Ini.GetStr("z", "default value", strKey, strSec);
char szValue[MAX_PATH];
if( !LT_get_str( "%z", szValue, sizeof(szValue) ) )
return 1;