Ошибка: Необработанное исключение типа: System.FormatException

// textBox1
            // 
            this->textBox1->Location = System::Drawing::Point(27, 8);
            this->textBox1->Name = L"textBox1";
            this->textBox1->Size = System::Drawing::Size(42, 20);
            this->textBox1->TabIndex = 0;
            this->textBox1->Text = L"15";
            this->textBox1->KeyPress += gcnew System::Windows::Forms::KeyPressEventHandler(this, &Form1::textBox1_KeyPress);
            this->textBox1->KeyUp += gcnew System::Windows::Forms::KeyEventHandler(this, &Form1::textBox1_KeyUp);
            // 
            // Form1
            // 
            this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
            this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
            this->ClientSize = System::Drawing::Size(725, 493);
            this->Controls->Add(this->panel4);
            this->Controls->Add(this->pictureBox1);
            this->Controls->Add(this->panel1);
            this->Name = L"Form1";
            this->StartPosition = System::Windows::Forms::FormStartPosition::CenterScreen;
            this->Text = L"Form1";
            this->Load += gcnew System::EventHandler(this, &Form1::Form1_Load);
            this->panel1->ResumeLayout(false);
            this->panel3->ResumeLayout(false);
            this->panel2->ResumeLayout(false);
            (cli::safe_cast<System::ComponentModel::ISupportInitialize^  >(this->pictureBox1))->EndInit();
            this->panel4->ResumeLayout(false);
            this->panel4->PerformLayout();
            this->ResumeLayout(false);

private: System::Void textBox1_KeyPress(System::Object^  sender, System::Windows::Forms::KeyPressEventArgs^  e) { 
            // this->Text=Convert::ToString(ToInt64(e->KeyChar));
            if (((e->KeyChar>=48) && (e->KeyChar<=57)) || (e->KeyChar==8)) razmer=Convert::ToInt64(textBox1->Text); else e->KeyChar=0;
                        }

private: void numericUpDown1_ValueChanged(Object^ sender, EventArgs ^ e)
{           
    размерКисти = numericUpDown1->Value;
}