On Linux and OS/2 there is a known problem using the lotus.domino.Document.replaceItemValue() API if the object is a number. Strings work correctly. The usual symptom of this issue is a java.lang.AbstractMethodError. This is caused by a bug in certain versions of the JVM on Linux and OS/2.
A workaround is to make all items Strings and do the appropriate conversion before setting (and after getting).
On Linux, using notesjre to replace the JVM with the latest IBM JDK 1.1.8 seems to solve this problem. However, this solution is untested and considered unsupported as of R5.0.3. On OS/2 there is no supported way to replace the JVM, so this issue currently has no workaround in terms of changing/upgrading the JVM level on OS/2.
NOTE: As of R5.0.7, testing shows that these particular errors no longer occur.