transfer .jpg file 5MB problem

Smartftp refused to do upload a .jpg file (+5MB), it did nothing at all.
but the same file zipped and with an equivalent size uploaded without any problem
+- System -----------------------------
Microsoft Windows XP Home Edition
Service Pack 2 (Build 2600)

CPU Speed : 1854 MHz
Total Memory : 446 MB
Free Memory : 160 MB

+- SmartFTP ---------------------------
Version : 3.0.1010.19
Time Stamp : 2008-03-20 20:05:01
Platform : x86

+- Application DLL --------------------
sfFTPLib.dll : 1.5.12.30
sfFavorites.dll : 1.0.6.19
sfFavoritesShellExtension.dll : 1.0.1.9
sfTransferQueue.dll : 1.0.3.19
sfFTPShellExtension.dll : 1.0.1.19

+- Language ---------------------------
SmartFTP.exe : 3.0.1010.19

+- Internet Explorer ------------------
Version : 7.0.5730.11

+- Winsock ----------------------------
Winsock : 2.2