Unreliable data stream

C, 168 characters

i;main(c){for(srand(&c);i++<3;putchar(rand()%10?i=0,c:c-126?c+1:33))c=getchar();
puts("ERROR CODE 4625: UNRECOVERABLE ERROR, PLEASE CONTACT YOUR SYSTEM ADMINISTRATOR");}

This solution's seeding of the PRNG takes advantage of the fact that modern OSes change the stack's location in memory on each run, as a basic measure against stack-smashing exploits.

Befunge-98, 166 159 156 155 148

This one improves on the other excellent Befunge answer with the correct probability (1/10) and is slightly more compact:

~>?#v?1+\1>+\:'~1+-4k#x07_$'!>,:3-!#v_
>#?>>>\$\0^>
^<<
A"##  "CT YOUR SYSTEM ADMINISTRATOR"<@,kM'"ERROR CODE 4625: UNRECOVERABLE ERROR, PLEASE CONT

Ruby, 156

e=3
putc(($_.ord-33+r=rand(10)/9)%94+33)/e=r>0?e-r :3while gets(1)rescue$><<'ERROR CODE 4625: UNRECOVERABLE ERROR, PLEASE CONTACT YOUR SYSTEM ADMINISTRATOR'