PKCS7 padding is invalid and cannot be removed

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:

Code:

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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;
                }

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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… ?