error while installing microsoft .net framework 3.5

[ibtesam]

Following error is encountered:


[05/02/11,07:34:25] Microsoft .NET Framework 3.0a: [2] Error:
Installation failed for component Microsoft .NET Framework 3.0a. MSI
returned error code 1603
[05/03/11,04:21:25] Microsoft .NET Framework 3.0a: [2] dlmgr:
CDownloadJobBITSImpl::RunToFinish() : BITS job in BG_JOB_STATE_ERROR
state.
Context: 5 Error code: -2145844841 Description: Proxy authentication
is required.

[05/03/11,04:21:25] Microsoft .NET Framework 3.0a: [2] Failed to fetch
setup file in CBaseComponent:reInstall()
[05/03/11,04:21:26] setup.exe: [2] ISetupComponent:re/Post/Install()
failed in ISetupManager::InternalInstallManager() with HRESULT
-2147467260.
[05/03/11,04:21:26] setup.exe: [2] CSetupManager::RunInstallPhase() -
Call to Pre/Install/Post for InstallComponents failed
[05/03/11,04:21:26] setup.exe: [2]
CSetupManager::RunInstallPhaseAndCheckResults() - RunInstallPhase()
returned a NULL piActionResults
[05/03/11,04:21:27] setup.exe: [2] CSetupManager::RunInstallFromList()
- RunInstallPhaseAndCheckResults failed [2]
[05/03/11,04:21:27] setup.exe: [2]
ISetupManager::RunInstallLists(IP_PREINSTALL failed in
ISetupManager::RunInstallFromThread()
[05/03/11,04:21:28] setup.exe: [2]
ISetupManager::RunInstallFromThread() failed in
ISetupManager::RunInstall()
[05/03/11,04:21:28] setup.exe: [2] CSetupManager::Run() - Call to
RunInstall() failed
[05/03/11,04:21:28] WapUI: [2] DepCheck indicates Microsoft .NET
Framework 3.0a is not installed.
[05/03/11,04:21:28] WapUI: [2] DepCheck indicates Microsoft .NET
Framework 3.5 'package' was not attempted to be installed.
[05/03/11,04:26:33] Microsoft .NET Framework 3.0a: [2] dlmgr:
CDownloadJobBITSImpl::RunToFinish() : BITS job in BG_JOB_STATE_ERROR
state.
Context: 5 Error code: -2145844841 Description: Proxy authentication
is required.

[05/03/11,04:26:33] Microsoft .NET Framework 3.0a: [2] Failed to fetch
setup file in CBaseComponent:reInstall()
[05/03/11,04:26:33] setup.exe: [2] ISetupComponent:re/Post/Install()
failed in ISetupManager::InternalInstallManager() with HRESULT
-2147467260.
[05/03/11,04:26:34] setup.exe: [2] CSetupManager::RunInstallPhase() -
Call to Pre/Install/Post for InstallComponents failed
[05/03/11,04:26:34] setup.exe: [2]
CSetupManager::RunInstallPhaseAndCheckResults() - RunInstallPhase()
returned a NULL piActionResults
[05/03/11,04:26:34] setup.exe: [2] CSetupManager::RunInstallFromList()
- RunInstallPhaseAndCheckResults failed [2]
[05/03/11,04:26:34] setup.exe: [2]
ISetupManager::RunInstallLists(IP_PREINSTALL failed in
ISetupManager::RunInstallFromThread()
[05/03/11,04:26:34] setup.exe: [2]
ISetupManager::RunInstallFromThread() failed in
ISetupManager::RunInstall()
[05/03/11,04:26:34] setup.exe: [2] CSetupManager::Run() - Call to
RunInstall() failed
[05/03/11,04:26:34] WapUI: [2] DepCheck indicates Microsoft .NET
Framework 3.0a is not installed.
[05/03/11,04:26:34] WapUI: [2] DepCheck indicates Microsoft .NET
Framework 3.5 'package' was not attempted to be installed.
[10/20/03,05:06:23] Microsoft .NET Framework 3.5 'package': [2] Error:
Installation failed for component Microsoft .NET Framework 3.5
'package'. MSI returned error code 1603
[05/05/11,18:13:13] Microsoft .NET Framework 3.5 'package': [2] Error:
Installation failed for component Microsoft .NET Framework 3.5
'package'. MSI returned error code 1603
[05/05/11,18:13:37] WapUI: [2] DepCheck indicates Microsoft .NET
Framework 3.5 'package' is not installed.

can anybody help me solve it