There are occasional glitches that arise during card play on internet sites. The most common ones are usually related to folding vs. calling/betting. Like you pre-click on "Call" and your hand is folded instead. Hate that. Or, I've heard of rare occasions when an inferior hand was awarded the pot. But these are usually isolated incidents. You certainly see them more on fledgling sites with questionable software than on big, established sites like PokerStars
, UltimateBet, or Full Tilt. But they CAN happen anywhere, anytime.
I echo Heshkak's query. What specifically happened that constituted an "invalid raise"? Not sure I've actually seen one of those myself.