PAsnOctetString = ^TAsnOctetString;
 TAsnOctetString = record
   stream: PByte;
   length: UINT;
   dynam: BOOL;
 end;

 PAsnAny = ^TAsnAny;
 TAsnAny = record
   asnType: BYTE;
   case Integer of      0: (number: TAsnInteger32);          { ASN_INTEGER, ASN_INTEGER32 }
     1: (unsigned32: TAsnUnsigned32);     { ASN_UNSIGNED32 }
     2: (counter64: TAsnCounter64);       { ASN_COUNTER64 }
     3: (str: TAsnOctetString);           { ASN_OCTETSTRING }
     4: (bits: TAsnBits);                 { ASN_BITS }
     5: (obj: TAsnObjectIdentifier);      { ASN_OBJECTIDENTIFIER }
     6: (sequence: TAsnSequence);         { ASN_SEQUENCE }
     7: (address: TAsnIpAddress);         { ASN_IPADDRESS }
     8: (counter: TAsnCounter32);         { ASN_COUNTER32 }
     9: (gauge: TAsnGauge32);             { ASN_GAUGE32 }
    10: (ticks: TAsnTimeticks);           { ASN_TIMETICKS }
    11: (arbitrary: TAsnOpaque);          { ASN_OPAQUE }
 end;

 TAsnObjectName = TAsnObjectIdentifier;
 TAsnObjectSyntax = TAsnAny;

 PSnmpVarBind = ^TSnmpVarBind;
 TSnmpVarBind = record
   name: TAsnObjectName;
   value: TAsnObjectSyntax;
 end;

 PSnmpVarBindList = ^TSnmpVarBindList;
 TSnmpVarBindList = record
   list: PSnmpVarBind;
   len: UINT;
 end;

procedure TMainFm.PrintVarBind(const VarBind: TSnmpVarBind);

var
 P: PByte;

with VarBind.value do
   case asnType of
...
     ASN_OCTETSTRING:
       begin
         A[2] := 'Octet String';
         if str.length > 0 then
         begin
           IsAscii := True;
           P := str.stream;
           for i := 0 to str.length - 1 do
           begin
             if not (P^ in [0, 32..127]) then    // <-- ТУТ ОШИБКА!!!
             begin
               IsAscii := False;
               Break;
             end;
             Inc(P);
           end;
...
 end;

PAsnAny = ^TAsnAny;
TAsnAny = record
  asnType: BYTE;
  case Integer of      0: (number: TAsnInteger32);          { ASN_INTEGER, ASN_INTEGER32 }
    1: (unsigned32: TAsnUnsigned32);     { ASN_UNSIGNED32 }
    2: (counter64: TAsnCounter64);       { ASN_COUNTER64 }
    3: (str: TAsnOctetString);           { ASN_OCTETSTRING } <-- Вот ОНО - str!!!
    4: (bits: TAsnBits);                 { ASN_BITS }
    5: (obj: TAsnObjectIdentifier);      { ASN_OBJECTIDENTIFIER }
    6: (sequence: TAsnSequence);         { ASN_SEQUENCE }
    7: (address: TAsnIpAddress);         { ASN_IPADDRESS }
    8: (counter: TAsnCounter32);         { ASN_COUNTER32 }
    9: (gauge: TAsnGauge32);             { ASN_GAUGE32 }
   10: (ticks: TAsnTimeticks);           { ASN_TIMETICKS }
   11: (arbitrary: TAsnOpaque);          { ASN_OPAQUE }
end;

SnmpMgrStrToOid(PAnsiChar(sOID), @OID);

with VarBindList do
   begin
     list :=  SnmpUtilMemAlloc(SizeOf(TSnmpVarBind));
     len := 1;
     list^.name := OID;
     list^.value.asnType := ASN_NULL;
   end;

RequestType := SNMP_PDU_GET;
   RetVal := SnmpMgrRequest(Session, RequestType, @VarBindList,
       @ErrorStatus, @ErrorIndex);

PrintVarBind(VarBindList.list^);

function SnmpMgrRequest(session: PSnmpMgrSession; requestType: Byte; variableBindings: PSnmpVarBindList;
 errorStatus: PAsnInteger32; errorIndex: PAsnInteger32): SNMPAPI; stdcall;

function SnmpMgrRequest; external  'mgmtapi.dll'  name  'SnmpMgrRequest';

 try
...
   if not SnmpMgrStrToOid(PAnsiChar(sOID), @OID) then
   begin
     Raise Exception.CreateFmt('Invalid Oids, ''%s'', specified.', [sOID]);
   end;
...
 finally
   SnmpMgrClose(Session);
 end;

var
 sOID: AnsiString;
begin
 sOID := '.1.3.6.1.2.1.1.1.0'; <-- это разве не ANSI ???
 SnmpMgrStrToOid(PAnsiChar(sOID), @OID);

SnmpUtilOidToA(@VarBind.name),

VarBindList