Presently, many users of Samsung Galaxy S Plus (including myself) reported a bug with their Google Market Place. The device can not update or download anything from Google Play Store. Its giving a downloading error-905 after completing 100% download, and the applications do not get installed or updated from the Google Play. Downloads and installs from other sources are working fine. (I tried installing true caller while this issue resided on my phone, it worked fine).
After some trials, i found some way to resolve this.
Here is what i did:
1) Go to "Application" (lower bottom right hand corner on the home screen) > Settings > Applications > Manage applications
2)Select the "All" tab
3) Scroll down and select Google Play Store
4) Select "Uninstall updates"
This will uninstall the Google Play Store, taking it back to older Market place.
After few minutes, it automatically gets updates, and resumes back to Google Play Store (yes, automatically).
But now when i download anything from Google Play, it works fine for me.
Please try this out and let me know if this works for you as well.