.Net Code Returning Different Result Than C# Code?

The following code in C# gives result "228452386"

UInt32 a;
int k = 0;
a = 0x9E3779B9;
a += (UInt32)(url[k + 0] + (url[k + 1] << 8) + (url[k + 2] << 16) + (url[k + 3] << 24));

After above code is ran, "a" contains "228452386" But the following same code in VB.Net results in "Arithmetic operation resulted in an overflow". Basically the last statement is returning value "1868983913" so the runtime error is generated.

Dim a As UInt32
Dim k As Integer = 0
a = &H9E3779B9UI
a += CUInt(AscW(url(k + 0)) + (AscW(url(k + 1)) << 8) + (AscW(url(k + 2)) << 16) + (AscW(url(k + 3)) << 24))

note the variable "url" in above code could be any string and it is same for both codes.

EDIT:When I run the following statements in both C# and VB.Net than they both return same value

C#
(UInt32)(url[k + 0] + (url[k + 1] << 8) + (url[k + 2] << 16) + (url[k + 3] << 24))
VB.Net
CUInt(AscW(url(k + 0)) + (AscW(url(k + 1)) << 8) + (AscW(url(k + 2)) << 16) + (AscW(url(k + 3)) << 24))

Both statements return value "1868983913" for "url" "info:microsoft.com". But when I run complete statement with a += ..then VB.Net gives error while C# returns value "228452386".