More information is needed.
Is this an assembly or a detail part file?
The syslog file will give a better explaination of why the system failed to save.
From past experience, let me do some guessing. This is an assembly and the log file will show that the assembly failed to save because a modified component was marked as modified, yet is a read-only part to you. Replace the read-only component with the unmodified one from disk and retry the save. If the reason for the modification is being opened in a newer version of NX, close the component from your loaded componets and do the save. This will preserve the assembly structure, but allow the assembly to save.
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