Two users having the same issue, both Notes 9.0.1, one on Win 7 64, one on OS X Mavericks.
Notes 9.0.1 was working fine but suddenly starts having display issues and generating error messages when opening Mail. Same mail file opens fine on other machines.
Running Notes in Basic mode avoids the problems. Re-installing Notes does not fix the issue with Standard mode.
Opened a PMR but no resolution so far.