I understand Resume language likes to be short and begin with the verb. I would suggest, "Credited with solving long standing software bug answering years of difficulty" Or "Solved long standing software bug solving years of difficulty" You could use resolving years of but I would hate to see both in the same sentence.
The unstated and primary part of the job description is always "Solving bugs". The least impressive resume sentence would be "Solved a bug for the employer." (Really! How proud you must be.) In your case, as you know, it is the fact that it has been around for years that makes it worth reporting. The bug must be described as long standing (or somehow) in order not to be ignored right off. It is not too exhaustive a description to be added even though the results following, essential to point out, tells us just how long standing. Making both statements in less than two phrases would be too terse even for a resume.
The age of the bug is answered in the second part, telling how what you did affected others. Very important.
I think using "Credited" tells them that everyone knows it was you who did it. We all solve bugs for a living. This one needs a bit of extra verbiage. Well done.