Why didn't Han know how to talk with the guard Captain when attempting rescue?

Question

In ANH episode 4 when Han and Luke broke into the detention cell to rescue Lea, they get a call on the com asking what's going on. Han stammers and stutters and asks how the guard is doing in the most conciliatory of tones. When that fails he shoots the console with his blaster. Is there any explanation for this lack of professionalism and ignorance of protocol considering he was retconned to be a former Imperial Officer?

Answer 1

According to the film's official novelisations, Han was nervous, he panicked and frankly, the guard had already heard too much to believe him. We have three version of the same event and they all stress that he just never had a chance.

After gesturing for the Wookiee to take up a position where he could cover the elevators, Solo took a deep breath and responded to the unceasing calls from the comlink.
“Everything’s under control,” he said into the pickup, sounding reasonably official. “Situation normal.”
“It didn’t sound like that,” a voice snapped back in a no-nonsense tone. “What happened?”
“Uh, well, one of the guards experienced a weapon malfunction,” Solo stammered, his temporary officialese lapsing into nervousness. “No problem now—we’re all fine, thanks. How about you?”
“We’re sending a squad up,” the voice announced suddenly.
Han could almost smell the suspicion at the other end. What to say? He spoke more eloquently with the business end of a pistol. - _{^{Star Wars: A New Hope - Official Novelisation}}

and

“Everything is under control,” he said in his best official, yes-I-belong-here voice. “Situation normal.”
“What happened?” a voice crackled through the still-smoking intercom. Han jumped as a spark shot out of it.
“Uh…we had a slight weapons malfunction.” His voice sounded painfully awkward to his own ears, so he could only imagine what the person on the other end was thinking. “But, um, everything’s perfectly all right now. We’re fine. We’re all fine here, now, thank you. How are you?”
He cringed. - _{^{A New Hope: The Princess, the Scoundrel, and the Farm Boy}}

and

Over the intercom, a voice asked, “What happened?”
“Uh … had a slight weapons malfunction,” Han said, trying to sound official. “But, uh, everything’s perfectly all right now. We’re fine. We’re all fine here now, thank you. How are you?” Han winced at the lameness of his own words. _{^{A New Hope: Junior Novelisation}}