diff --git a/pkg/core/transaction/witness_condition.go b/pkg/core/transaction/witness_condition.go
index 316922605..71fcc1d33 100644
--- a/pkg/core/transaction/witness_condition.go
+++ b/pkg/core/transaction/witness_condition.go
@@ -549,7 +549,7 @@ func unmarshalArrayOfConditionJSONs(arr []json.RawMessage, maxDepth int) ([]Witn
 	if l == 0 {
 		return nil, errors.New("empty array of conditions")
 	}
-	if l >= maxSubitems {
+	if l > maxSubitems {
 		return nil, errors.New("too many elements")
 	}
 	res := make([]WitnessCondition, l)
diff --git a/pkg/core/transaction/witness_scope.go b/pkg/core/transaction/witness_scope.go
index 945fd3e92..5daf15eaa 100644
--- a/pkg/core/transaction/witness_scope.go
+++ b/pkg/core/transaction/witness_scope.go
@@ -1,6 +1,6 @@
 package transaction
 
-//go:generate stringer -type=WitnessScope -output=witness_scope_string.go
+//go:generate stringer -type=WitnessScope -linecomment -output=witness_scope_string.go
 import (
 	"encoding/json"
 	"fmt"
@@ -23,7 +23,7 @@ const (
 	// CustomGroups define custom pubkey for group members.
 	CustomGroups WitnessScope = 0x20
 	// Rules is a set of conditions with boolean operators.
-	Rules WitnessScope = 0x40
+	Rules WitnessScope = 0x40 // WitnessRules
 	// Global allows this witness in all contexts (default Neo2 behavior).
 	// This cannot be combined with other flags.
 	Global WitnessScope = 0x80
diff --git a/pkg/core/transaction/witness_scope_string.go b/pkg/core/transaction/witness_scope_string.go
index 5f6666af1..805ac1473 100644
--- a/pkg/core/transaction/witness_scope_string.go
+++ b/pkg/core/transaction/witness_scope_string.go
@@ -1,4 +1,4 @@
-// Code generated by "stringer -type=WitnessScope -output=witness_scope_string.go"; DO NOT EDIT.
+// Code generated by "stringer -type=WitnessScope -linecomment -output=witness_scope_string.go"; DO NOT EDIT.
 
 package transaction
 
@@ -20,7 +20,7 @@ const (
 	_WitnessScope_name_0 = "NoneCalledByEntry"
 	_WitnessScope_name_1 = "CustomContracts"
 	_WitnessScope_name_2 = "CustomGroups"
-	_WitnessScope_name_3 = "Rules"
+	_WitnessScope_name_3 = "WitnessRules"
 	_WitnessScope_name_4 = "Global"
 )
 
diff --git a/pkg/network/message_string.go b/pkg/network/message_string.go
index 2ebdacd9b..8e516f377 100644
--- a/pkg/network/message_string.go
+++ b/pkg/network/message_string.go
@@ -62,7 +62,7 @@ var (
 
 func (i CommandType) String() string {
 	switch {
-	case i <= 1:
+	case 0 <= i && i <= 1:
 		return _CommandType_name_0[_CommandType_index_0[i]:_CommandType_index_0[i+1]]
 	case 16 <= i && i <= 17:
 		i -= 16
diff --git a/pkg/rpc/server/server.go b/pkg/rpc/server/server.go
index a60feace1..ea9a6c15e 100644
--- a/pkg/rpc/server/server.go
+++ b/pkg/rpc/server/server.go
@@ -1675,7 +1675,7 @@ func (s *Server) getInvokeScriptParams(reqParams request.Params) (*transaction.T
 	if len(reqParams) > 1 {
 		signers, witnesses, err := reqParams[1].GetSignersWithWitnesses()
 		if err != nil {
-			return nil, false, response.ErrInvalidParams
+			return nil, false, response.WrapErrorWithData(response.ErrInvalidParams, err)
 		}
 		tx.Signers = signers
 		tx.Scripts = witnesses
@@ -1684,7 +1684,7 @@ func (s *Server) getInvokeScriptParams(reqParams request.Params) (*transaction.T
 	if len(reqParams) > 2 {
 		verbose, err = reqParams[2].GetBoolean()
 		if err != nil {
-			return nil, false, response.ErrInvalidParams
+			return nil, false, response.WrapErrorWithData(response.ErrInvalidParams, err)
 		}
 	}
 	if len(tx.Signers) == 0 {