PKCS7 padding is invalid and cannot be removed

[d00_ape]

Hi. I’m trying to dectypt a string I got from my supplier.

We have a common password and I got a string to decrypt using

System.Security.Cryptography.RijndaelManaged

Here is my decrypt function:

public string DecryptWithRijndael( string Key, string strDecode )
		{
			
			ASCIIEncoding textConverter = new ASCIIEncoding();
			RijndaelManaged myRijndael = new RijndaelManaged();         
			// set mode
			myRijndael.Mode = CipherMode.ECB; // Set mode
			myRijndael.Padding = PaddingMode.PKCS7; // Set padding         
			byte[] key = textConverter.GetBytes(Key);   //Create a new key and initialization vector
			
			// Get final key and initialization vector
			myRijndael.Key=key;
			myRijndael.GenerateIV();
			
			byte[] IV = myRijndael.IV;
			
			byte[] encrypted = Convert.FromBase64String( strDecode );

			//Get a decryptor that uses the same key and IV as the encryptor.
			ICryptoTransform decryptor = myRijndael.CreateDecryptor(key, IV);

			
			//Now decrypt the previously encrypted message using the decryptor
			// obtained in the above step
			MemoryStream msDecrypt = new MemoryStream(encrypted);
			CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read);
			byte[] fromEncrypt = new byte[encrypted.Length];
			
			//Read the data out of the crypto stream

			csDecrypt.Read(fromEncrypt, 0, fromEncrypt.Length);
			
			//Convert the byte array back into a string
			string sDecoded = textConverter.GetString(fromEncrypt);
			return sDecoded;
		}

On the line:
“csDecrypt.Read(fromEncrypt, 0, fromEncrypt.Length);”

I got the following message:

An unhandled exception of type 'System.Security.Cryptography.CryptographicException' occurred in mscorlib.dll
Additional information: PKCS7 padding is invalid and cannot be removed.

Any tip on what I may have done wrong… ?