Speedy Hire (LON:SDY) warned on annual profits and said its chief executive was quitting after problems led to a slower-than-expected start to the year.
The plant hire group predicted results for 2016 materially below its expectations for the year and 2015 results without a better revenue trend and successful implementation of recovery measures.
It said Mark Rogerson has decided to step down as chief executive and had been replaced by finance chief Russell Down.
Speedy blamed a lack of available equipment during a network improvement programme for lower revenue.
The rental company said it had spent too much time focusing on "strategic accounts" rather than small business customers.
It also said customer service had suffered from disruption during the implementation of a new IT system. Speedy said core hire trading across strategic accounts remained strong.
But it said talks with a third party about the potential sale of its remaining oil & gas business in the Middle East had failed to reach a satisfactory conclusion and had been discontinued. It is considering alternative options.
Jan Åstrand, who was appointed non-executive chairman in late-2014, will become executive chairman and plans to revert to non-executive status at Speedy's interim 2016 results in November 2015.
Åstrand said: "This is extremely disappointing. I believe Speedy remains a fundamentally good business but, whilst some progress has been made over the last year, the remedial action programmes have not been delivered as needed.
"Our immediate priority is to accelerate the execution of those programmes and realise the upside we believe they will deliver over the medium term. Additionally, we will increase our focus on the (small and medium sized business) core hire market.
"Improving performance is our top priority. We expect to be able to provide an update when we issue our H1 FY2016 pre-close statement in the last week of September."
Speedy shares fell 22.5p or nearly 32% to 48.25p.
Sanlam Securities analyst Andy Brown said: "This is clearly not good news and, while these are stock-specific issues, following on from the HSS Hire warning earlier this week, (it) will send shock waves through the sector."