java error 1330

ermm i dont know if i ment to be posting this on here but oh well

basicly when i try to download java its says that "We encountered an issue while trying to automatically install Java software onto your machine."

so i clicked install ofline or somthing like that and then it says after a while of downloading..."Error 1330.a file that is required cannot be installed because of the cabinet file c:\documents and settings\owner\application data\sun\java\...\data1.cab has an invalid digital signature this may indicate the cabnit file is corrupt."

oh and when i try to play runescape it comes up as a grey box witch is quite anoying

any help would be helpful