anti-phosphotyrosine blot on 2mo old samples? - (May/01/2009 )

we collected some IP samples and immediately ran a Western with anti-phosphotyrosine and it looked beautiful....2 months later we ran the exact same samples and the anti-phosphotyrosine blot looks awful - TONS of background.
I realize there could be a number of issues that promote high background, but the anti-PY is new to me so I'm wondering - is this a typical problem?

Personally, I've never reused samples.
I run IP samples or whole cell lysates on gel and then proble for Phosphorylation.
The quality of the extract for this type of probing changes over time. Proteins degrade, phosphorylation is lost etc.