Hi Joshualo,
Please install .NET Framework 4.0 instead of 4.5. You can download it from:
http://www.microsoft.com/en-us/download/details.aspx?id=17851
If that doesn't work, please wait till Monday, the new version (v1.0.0.9) will have XP support.
Let us know if there's anything else we can do for you.
the update doesn't work for me

Following are the details of the error:
PLATFORM VERSION INFO
Windows : 5.1.2600.196608 (Win32NT)
Common Language Runtime : 4.0.30319.239
System.Deployment.dll : 4.0.30319.1 (RTMRel.030319-0100)
clr.dll : 4.0.30319.239 (RTMGDR.030319-2300)
dfdll.dll : 4.0.30319.1 (RTMRel.030319-0100)
dfshim.dll : 4.0.31106.0 (Main.031106-0000)
SOURCES
Deployment url :
http://subrepo.com/install/SubRepo.application
ERROR SUMMARY
Below is a summary of the errors, details of these errors are listed later in the log.
* Activation of
http://subrepo.com/install/SubRepo.application resulted in exception. Following failure messages were detected:
+ Exception reading manifest from
http://subrepo.com/install/SubRepo.application: the manifest may not be valid or the file could not be opened.
+ Manifest XML signature is not valid.
+ SignatureDescription could not be created for the signature algorithm supplied.
COMPONENT STORE TRANSACTION FAILURE SUMMARY
No transaction error was detected.
WARNINGS
There were no warnings during this operation.
OPERATION PROGRESS STATUS
* [2014-3-24 12:11:07] : Activation of
http://subrepo.com/install/SubRepo.application has started.
ERROR DETAILS
Following errors were detected during this operation.
* [2014-3-24 12:11:08] System.Deployment.Application.InvalidDeploymentException (ManifestParse)
- Exception reading manifest from
http://subrepo.com/install/SubRepo.application: the manifest may not be valid or the file could not be opened.
- Source: System.Deployment
- Stack trace:
at System.Deployment.Application.ManifestReader.FromDocument(String localPath, ManifestType manifestType, Uri sourceUri)
at System.Deployment.Application.DownloadManager.DownloadDeploymentManifestDirectBypass(SubscriptionStore subStore, Uri& sourceUri, TempFile& tempFile, SubscriptionState& subState, IDownloadNotification notification, DownloadOptions options, ServerInformation& serverInformation)
at System.Deployment.Application.DownloadManager.DownloadDeploymentManifestBypass(SubscriptionStore subStore, Uri& sourceUri, TempFile& tempFile, SubscriptionState& subState, IDownloadNotification notification, DownloadOptions options)
at System.Deployment.Application.ApplicationActivator.PerformDeploymentActivation(Uri activationUri, Boolean isShortcut, String textualSubId, String deploymentProviderUrlFromExtension, BrowserSettings browserSettings, String& errorPageUrl)
at System.Deployment.Application.ApplicationActivator.ActivateDeploymentWorker(Object state)
--- Inner Exception ---
System.Deployment.Application.InvalidDeploymentException (SignatureValidation)
- Manifest XML signature is not valid.
- Source: System.Deployment
- Stack trace:
at System.Deployment.Application.Manifest.AssemblyManifest.ValidateSignature(Stream s)
at System.Deployment.Application.ManifestReader.FromDocument(String localPath, ManifestType manifestType, Uri sourceUri)
--- Inner Exception ---
System.Security.Cryptography.CryptographicException
- SignatureDescription could not be created for the signature algorithm supplied.
- Source: System.Security
- Stack trace:
at System.Security.Cryptography.Xml.SignedXml.CheckSignedInfo(AsymmetricAlgorithm key)
at System.Security.Cryptography.Xml.SignedXml.CheckSignature(AsymmetricAlgorithm key)
at System.Security.Cryptography.Xml.SignedXml.CheckSignatureReturningKey(AsymmetricAlgorithm& signingKey)
at System.Deployment.Internal.CodeSigning.SignedCmiManifest.Verify(CmiManifestVerifyFlags verifyFlags)
at System.Deployment.Application.Manifest.AssemblyManifest.ValidateSignature(Stream s)
COMPONENT STORE TRANSACTION DETAILS
No transaction information is available.