.NET (Core and Framework)

private const string _patternReturnDataSet = @"\A\d{2}[\s\t]+(?<Column>\w+[,\t]\d+[,\t]\d*[,\t])+[\n\r\f]+(?<Row>(?:[^,\t\n\r\f]*[,\t])+[\n\r\f]+)*{DONE}\z";
private const string _patternReturnVariant = @"\A\d{2}[\s\t]+(?<Text>.[^\t]*){DONE}\z";
private const string _patternError = @"\A\d{2}[\s\t]+(?<ErrorMessage>.[^\t]*)[\s\t]+(?:.[^,]*,[\s\t])*(?:.[^;]*;)[\s\t](?<ErrorNumber>\d*)[;][\s\t]+{DONE}\z";
private const string _patternInvalidCommand = @"\A(?:\d{2}[\s\t]+)?(?<ErrorMessage>.[^;]*)[;\s\t]+{DONE}\z";
private const RegexOptions _options = RegexOptions.Compiled | RegexOptions.CultureInvariant | RegexOptions.IgnoreCase | RegexOptions.Multiline;

Other than that, I changed this       V  from a + to a * and it seems to work
@"\A\d{2}\s+(?'ErrorMessage'.[^\t]*)\s*(?:.[^,]*,\s)*(?:.[^;]*; )\s(?'Number'\d*);\s+{DONE}\z"
I would also remove these   ^             ^             ^

I guess not, so I added the SPACE.

Manas Bhardwaj wrote:

There is no need of multi threading...